I'm planning a talisman for my first ever character, and I'm starting to think that too many Form and Material Bonuses are a trap, as it's unlikely that she will be able to attune them all (and Consumate Talisman is off the table)
So I'd like to know, what attunements have people found most useful? Those that play to that Maga's strengths or shore up weaknesses? or are some so good that it's always a good idea to have them.
Bob
Too many variables to answer definitively.
What is your mage's focus? What do they want to boost?
I like bonuses to the Arts, altho' those are usually pretty small. There are some massive bonuses to some very narrow categories - no brainers if they fall in the path of your mage's interests.
Nah, not a trap - you'll open those that matter, and just ignore the rest. First prioritize what's important, get those on board, and anything extra that comes along for the ride is gravy for "some day". 
It's not a trap. Attuning a bonus can happen whenever you add an enchantment to your talisman. So they can build up rather quickly if you're actively inserting effects into your talisman. I also allow attunement when someone adds more vis to their talisman, although I don't think that's explicit.
Yes. 
A talisman is a highly unique item, individual to the magus. Perhaps building them as one would build a new magus isn't a bad move. Effects for offense, defense, utility, senses and movement are good effect categories to look at.
If you can afford a single component, go for mercury.
But as the other posters say, bonuses can add up rather quickly. They will never be massive in the bonus they provide (except for banishing demons and a few other things) but they can get a nice addition to your casting and lab totals. I tend to use them to supplement my weak areas so they are weak, but not so weak, while other members of my troupe go for the specialized talisman in doing one thing, either boosting their specialization area or providing bonuses that add up to have a secondary specialization area almost as strong as the first one.
I didn't think they added to Lab totals...
Well, not to Lab Totals, you're correct.
Hmm... I might have been doing this wrong for years... Will need to check.
Well, it could be one of Xavi's Breakthroughs... 
Or your troupe house rules that it does.
Patricia Fabulator
House Mercere, ReTe specialist (eventually; she doesn't want to be, but feels guilt-tripped into it so that the house has someone who is able to cast Hermes's Portal)
She really wants to be a wanderer and travel writer, and learn lots of languages and area lores
So mercury would be great if it added to Lab Totals, but casting totals only is also going to be necessary.
What I've got so far is:
A necklace: chain is Copper and Lead chased to look like pin feathers and quills, with a magnet clasp the pendant is an Iron Cross, front faced with clear glass . The cross contains mercury to reflect the glory of creation, and the iron on the top is shaped into a crown of thorns, and on the back is carved a sun scarab, written round are the sigils of angels.
Studded into the crown are a Garnet, an Opal, Cinnibar, and Frankincense
Which with her current MT of 4 is a bit of a long way off.
I honestly don't see the use of that many shape and material bonuses, especially if they can't be used for lab work (She's cast so few spells in play that the other charcters suspect her of being a redcap!)
But the main point of my question was for general advice rather than specific to my campaign; how many bonuses have you actually attuned in play, and which have you found most useful?
Bob
The most useful ones are the ones that correspond to spells that the maga often uses? There is also something to be said for attunements that are in areas your maga isn't great at, but nonetheless would like to cast occassionally. A small Casting Total bonus is often worth a lot more in your off-suit TeFo combinations than it is in your TeFo speciality.
But there is no cost to adding attunements, so just add one in whenever you enchant an effect into your talisman (until you are out of valid attunements).
I think that the most generically useful ones are the one for wands/staff around controlling/destroying stuff at a distance and using projectiles, which I guess explains why the "traditional" talisman is a staff/wand. But only if your maga is going to be casting spells that can use this sort of bonus.
BTW, atttunements don't add to Lab Totals (last paragraph of Talisman Attunement section, ArM5, page 98).
Ahh but there is a second order cost, namely if I am designing a talisman, the number of components is limited by the MT if the Maga in question, so there is a trade-off, how long do you spend dragging your MT up to double digits (during which time you don't have a talsiman) vs having lots of goodies to attune later.
My prospective Taliman above has (I believe ) 55 possible attunements (some of which partially overlap). I don't expect to get anywhere near that number of seasons working on my talisman, so I was wondering about what a typical number of attunements would be in a played saga (not a theoretical maximum) to see if I had been woefully overoptimistic.
Bob
In my experience, only up to half a dozen attunements actually get done. Also see the magi in Magi of Hermes and various other supplements.
It is certainly possible to have many more, but one initial attunement plus one done when each of four or five effects are added seems typical.
Basically, I wouldn't bother chasing the opportunity for many, many attunements. Pick a thing to make your talisman out of that has a few handy attunements available.
Ditto.
If you get above that, you might consider destroying your old talisman and going for a new one later in your career.
(He has a lot of those, iirc...)
55?! 
That ~sounds~ like a lot - how many components is that?
And "MT to double-digits" - not necessary, imo. And for exactly the reason you're mentioning - overkill of # of components. Now you ARE looking at bonuses that you might never get around to seeing, even if you just open 1 attunement/component.
The only reason to wait to get a larger MT is that you want/need more components as part of a compound item (which is almost(?) always the way to go w/ a Tali'). If your MT goes up later, you can add to the maximum number of pawns (& so max # of levels of spell effects) that you can put into it, but you can't add components later. So that's the only consideration - did you get what you wanted there (or close enough) when you first built it?
I'd judge that most of my magi build their tali' when their MT is around 5-7*, altho' some will have Puissant MT on top of that. That's 6-8 "components", each possibly with multiple potential bonuses (& +2 more components if Puissant). Maybe that's early vs. some others, but I like to have that Tali up and running sooner than later. Waiting until you're an archmage... too late, imo.
(* I had one who built a small Tali very early, MT 3 or so, something quick and dirty to grab some large special-purpose bonuses early, planning on reforging a new one later. That worked well for him - he did have a couple very impressive Casting Totals early as a young mage. Admittedly, it was not un-painful to destroy it and spend the time to build a new one later, and go over much of the same territory a second time. Not for every character, but it worked for him. )
Again, too many variables.
Does your SG encourage and allow all the labwork you could want, or do they pull the magi away from their labs (usually kicking and screaming, I'd assume) for seasons at a time? If they do have free time, Is your mage a labrat or an "adventurer" (loosely speaking)? And ~if~ they are in the lab - are they improving their Tali', or working on something else?
But unless the Tali is going to be THE focus of the mage whenever they are in the lab, I wouldn't count on more than a half-dozen attunements for a long time, and quite possibly fewer. 1 attunement when they create the thing, +1 for each spell effect invested... and... are they going to spend a season just to get another attunement?
When I plan a Tali', I plan the thing - I know every last power that I want into it, as designed, and what will be "next" once MT increases (by X amount). Figure that out, and that will tell you about how many different individual attunements you'll be able to open (without spending a season only to that purpose).
I generally find a lot of magi's talismans to be odd, because they ignore the greatest advantages of a talisman; they extend your reach and they have your magic resistance. I'd gladly sacrifice most of the Shape and Material bonuses for odd materials to get an extra 5 feet of Touch Range or have my Parma Magica covering the contents of a sack. Rope, Chain, Staff, Cloak, Sword, Belt, Bag/Sack ("Wind, Fire, all that kind of stuff!") these are the most useful talisman attunements.
Just don't botch on that attempt to touch (hit) with your staff.
I have seen quite a few staffs that transform to bags and viceversa. Utility cloaks (transportation, wrapping protection and healing the covered area) are also popular. Staffs,m wands and swords still win around here, though.
I was planning on a hammer with a wrench bit at the other end, with a spell on it to resize it. I mostly work with mundane stuff, so 
+1
I designed a chain-wielding Flambeau with a lot of Touch spells, but have never played him. With the right effects, the chain can even stretch out and be guided accurately at some distance. Good even for "touching" spirits and other things that you wouldn't want to get close to.
(A sack... interesting...)
Yeah, one of the very first enchantments that usually find their way onto my Talismans is something simple that makes them "tough as iron".
Well, botching could result in the staff/item falling into the opponent's hands. And if that's a magus or a powerful demon, perhaps, it's not a good thing...