Suppose for instance that you put a ReHe spell on a carpet to make it move however you want. How many people or how much weight could you put on top of it before it would not rise or move?
One answer would be to figure out the weight of an "individual" of the Form, and use that as your answer. A 1 cubic pace of hardwood weighs (iirc) about 1500 pds (680 kg) or so. (Tho' a "plant" a pace in measurement would weigh maybe 3% of that!)
But perhaps a more practical approach is to spin off from the Central Rule, perhaps in conjunction with that - which is, no more than seems reasonable.
Every such spell effect should have a defined limit. I designed a ReHe "flying broom" spell that can only carry 2 people max - seems about right for the effect, despite the weight suggested above. (To be able to use the lowest possible magnitude of that spell effect to fly a branch and 6 people sitting on it just seems "too much" imo.)
If a player had a flying carpet, as a SG I would recognize several problems with the spell - not the least is "staying on the carpet!", which is hardly guaranteed! But a large carpet might lift 4, maybe 6 people - that seems to fit with the concept.
A related question is "how fast" is that first level of Regio, and how much faster do additional levels make it? I would say the "as fast as smoke rises" guideline (from ReCo) seems about right - but most ReFo attack spells do not match this. Perhaps there is some Velocity vs Mass relationship? That's for each SG/Troupe to decide - just be consistent, and expect players to take it to extremes.
Some of the varied considerations for such long-distance flying effects (and yes, I've put thought into this before) are...o Not falling from the "conveyance"
o controlling the "conveyance", and its maneuverability (esp re #1!)
o staying warm, dry and alert after hours of high winds and cold weather
o truly "bad" weather, like flying into a storm
o navigation in a world with no useful maps and few visible landmarks like paved roads
This last, especially, should not be underestimated, as it may be ~the~ limiter for casual use of such. Today, we take air-travel and navigation for granted - in ME, without some spell to aid you, it would either be a series of short hops, or low-level following of a muddy track called a "road", or possibly flying until you hit a major landmark (major river, coastline), then turning and following that, and stopping at the first civilization and asking "Hey! Whar in tarnation are we?!" (and hope they speak Latin...) 
Even hopping from one major city to one close nearby is difficult without a spell or landmark to follow, because the "compass heading" of one from another is not something that anyone but a flying mage would need to know.
As an aside, many magi probably do follow the roman roads when flying, as they went everywhere, are fairly ubiquitous, and are most certainly paved. Many are still functional today. I would expect that although maps are uncommon amongst the mundane population, Redcaps probably have quite good maps.
-Ben.
Magic! 
Give it a muto requisite, and now the carpet has the strength of steel. Or, take a page out of the Black Company series and put your carpet on a nice wooden platform. Ah, but you're not concerned with the integrity of the carpet so much, are you?
a 1-pace cube of wood is going to be pretty heavy, so I'd say that a spell on a carpet could handle at least two, maybe three people. By adding a magnitude you could increase that amount by whatever your SG deems appropriate-- personally, I'd say the magnitude would allow you to carry the weight-equivalent of another five people, assuming that you have space on the carpet to accomodate them.
-Ben.
Roman roads outside Italy are rare in ME. Many paved roads were destroyed by the people who lived near them, who had better uses for dressed stone than roads. Most of the Roman roads have been abandoned for the meandering trade roads that preceeded them. Bridge failure, particularly, makes Roman roads useless in many areas.
The "Roman roads still functional today" are those in high-trade areas where there was a strong enough ruler to warrant the expense of road maintainence for trade. This is true in parts of Italy and France, and virtually nowhere else in the West.
I thought England had a fair share of functional Roman roads. Even so, I guess that leaves North Africa, Spain, and the Transalpine roads out. Either way, depending on where you set things up, the existing Roman roads, however many you decide there are and where they are, would still work nicely for aerial navigation.
-Ben.
Your Roman Road Mileage May Vary.
England, and most everywhere in Europe, has examples of functional roman roads, even some stretches that may possibly be still in use (or were until modern preservationist sensibilities took over), but as a "from point A to point B" continuous ribbon? Very rare (outside some areas, as mentioned above.)
Many of the existing longer stretches were uncovered recently, and were isolated stretches far from historical populations, that were covered over and thus preserved, and then unearthed recently.
(Also, I'm not sure how willing a mage would be to have their flying carpet so low that they could follow a road, Roman or not, especially if it were to go thru a forested area. It might upset the locals. It might even attract the rare bow shot. Individual priorities would, of course, vary.)
Do not forget to lower your parma! Or give your flying carpet a penetration high enough to penetrate your MR. Otherwise it will not carry you anywhere...
Exeption: You make it your talisman.
(will that debate never cease) 
(unlikely)
No, it doesn't. It has patches, but the bridges in England haven't survived so the roads to those bridges have been abandoned. English roads are a classic case of locals not bothering to repair them, because trade is done by ship, so there's no point in keeping the roads open.
The Transalpine road is so bad that there is an order of monks dedicated to saving the poor people using them, and locals spend a huge amount of money replacing the route in 1222, by opening the Saint Gotthard's Pass. North Africa I admit to not knowing much about.
The Roman Roads in Spain have some pieces where the road is still used. Bits are incorporated into the route of the pilgrimage to Saint James for example, but basically a road, to be maintained, needs trade to flow along it and the Conquest and Reconquista stuff that up, because a couple of the major Roman roads in Spain route through Cadiz, and Cadiz isn't really all that important to traders for several centuries between the 700s and 1200s.
Which is to say, sorry, but no, Roman roads have been largely abandoned in Mythic Europe. I can see that they would make aerial navigation easier, sure...
-Ben.
[/quote]
Bah! If a magical bridge can be walked upon, then a magical carpet can be sat upon.
Mark
I seem to have stirred up a hornets' nest. 
Sorry for that.
Just one remark and I will never touch that subject again:
A magical carpet can surely sustain a magus but I cannot see how movement of that carpet can be transmitted to a person with MR when a stone moved my magic cannot transfer momentum to the target with MR.
However, pondering the problem I thought about original reseach:
A new modification of effects invested in items that allows the effect to ignore the creator's (and only the creator's) MR when a arcane connection in embedded in the artefact. This way you can create objects that ignore you MR to use effects you do not want to invest in your Talisman but it has the same draw backs as it leaves an acrane connection to you. I would thin this to be in between a minor and major breakthrough.
Well the answer is clearly, "It's magic!" Or perhaps it's that momentum doesn't exist, although I haven't looked through Art and Academy recently, though. Or maybe you should just accelerate slowly and hold on before turning.
Exactly
The next time your mage is on a ship, I'll be sure to enchant it with some ReHe, and see what happens.
There is a point where "modern logic" and understanding of physics and cause and effect has to give way to allow one to tell the story. Welcome to that point. 8)
There is no such thing as momentum in an Aristotlean universe. Or, as other people would have it: "it's magic!".
Mark
I'm wondering about the medieval understanding of friction....
if Friction is in paradigm the If you could somehow enchant the road to be magical without any effect (magic shell) then with a little effort you could sail your parma'd magi down the road like a boat.
you can still stand on the road, but would there be conact/friction
A