But neither of these reduce any botch dice from the finesse roll.. Only "careful with Finesse" does. And even if someone has taken that virtue, he might not botch but roll a 0, thus letting him slip and fall on arrival. There are many evil things I could think of that might happen.... 
(Not just falling from a cliff but also falling in a way that damages a magic item or -beware- your talisman!!!! 
- Cautious Sorcerer reduces botch dice, but never to fewer than one. This reduction is applied first, so other botch-reducers may eliminate the possibility of botching.
- Cautious with (Ability) reduces botch dice, and can reduce to zero botch dice. This would include Cautious with Finesse.
- A familiar's Golden Cord reduces botch dice, but never to fewer than one. (Presumably this combines with other botch-reducers like Cautious Sorcerer, but that's not spelled out unless it's in the errata, which I didn't check.)
- Mastered spells cast in a non-stress situation don't botch at all.
- Mastered spells cast in a stress situation have reduced botch dice, which may eliminate the possibility of botching.
I'd rule that tactical teleportation is always a stress situation, at least for the Finesse roll. Teleporting from a safe place into combat can be non-stressed for the casting roll, however. A bad finesse botch might put the caster into the path of an attack (including "friendly fire"), but it doesn't risk Twilight or other magical botch problems.
I'd say that non-combat teleportation doesn't require a Finesse roll, unless there's something stressful about the teleportation other than combat. Teleporting into a familiar room in a safe-house would not require Finesse. Teleporting onto a narrow window-sill high up on a tower would require Finesse. Teleporting into a clear spot in a busy marketplace wouldn't require Finesse for the teleport, but would require it to time the teleport to a moment when no one was looking at the destination spot.
If teleportation were used so much that it started to look like a story-breaking exploit, I might rule that teleportation is always a stress situation, unless the caster can see the destination without concentration. So if a magus created a Diameter-duration Summoning the Distant Image variant, the teleportation roll would be non-stressful. However, the botch risk would remain for the variant Distant Image, unless the magus mastered that too. However, between botch-reducing virtues, a familiar Cord, a spell created specifically to reduce botch risk, and mastery of both spells, I'd say a magus deserves the possibility of teleporting without a botch roll. At that point, the magus is practically a walking Hermes Portal.
Speaking of Hermes Portal, by the way, I thought of something that might be a more efficient means of accomplishing the same goal. But that will require some figuring, and probably deserves its own message anyway.
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It's called seven league stride, and allows you to travel to any location in sight
You could allways rule it as D&D teleporting with the possibility of appearing to high or to low. Materializing once with his lower legs mixed with the stone should slow down his use of teleporting to unknown areas if he survives the 1st error.
Not in there at all, and even if it was remember the key rule that the books are just a suggested guide and you should moddify or not use any parts that you dont like.
Personally I think a nice watching ward to detect anyone teleporting in as a trigger would be fun to use
Oops, overlooked that one. I was thinking it required arcane connection, but was limited to seven leagues.
The description in the book points mentions "in a wall" as a possible consequence of a botched Finesse roll.
Now that you mention it, I can't find any evidence of this rule in the book. Apparently it's been a house rule so long that no one in our group ever thought to mention that it wasn't specifically stated in the rules.
Not that I'm particularly fond of the "nightcrawler" battlemage idea, but purely from a mechanics point of view, why would you use a base 30 spell designed to take a target up to 21 miles, when a base 10 spell would be more suitable for close area teleporting?
At the most you might make it base 15 if 5 paces was too close for comfort. Up to 50 paces would be more than sufficient and perhaps even that a bit further than one would wish to be if engaged in battle (almost the entire length of an American Football field ~80 yards or 240 feet).
Good point, BoXer. A lower-magnitude spell would definitely make more sense for tactical teleportation. Magical botches are always a risk, and a lower-powered spell would reduce that. One might even argue that an easier spell would make the target a bit easier on the Finesse roll, on grounds that the easier spell is leaves the magus more chance to think about ending up in just the right spot.
Tactical teleportation is still risky, but with an easier spell it drops down to the range of normal risk of battle, rather than the greater risk of casting a heavy-duty spell under stress conditions. Even with that ability, one wouldn't want to use it a lot, because each casting costs a combat round that might be used to attack the enemy, whether with spells or mundane attacks.