I use that very thing for taming - I've got a built cage near the kennels, with an animal stockpile designated around it such that the four squares adjacent to the cage are part of the stockpile, and no other squares are. That stockpile accepts only tameable things. So, dwarves automatically drop caged animals next to the taming cage, and when an animal is transferred, they remove the empty cage and bring along another animal-in-a-cage.
In my experience, there's a small (perhaps 25%) chance of an animal escaping when transferred between adjacent cages, but pretty much a 100% chance of an animal or monster escaping if someone tries to drag it somewhere from a non-adjacent cage. There's also a chance of a monster escaping when someone picks up his cage to take it to the trade depot, and another chance to escape when it's deposited at the trade depot. (I gave up on trying that after several ratmen escaped at the trade depot and scared away the elven traders)
I have also seen some goblin thieves who consistantly refuse to try to get free when being dragged from cage to cage. In particular, I had one goblin thief who had a dwarf child in his bag - This particular goblin got dragged from his cage to another one 30 or 40 spaces away, and then dragged back to another cage, and again two or three more times, and he never tried to get away. I can only presume that he was smarter than the rest of the thieves, who were all shot dead before they could get further than one space from their cage. The ones who refused to try to run away, however, were left alone by the marksdwarves.
In the end, I had around four thieves who refused to try to run away, and so I had the dwarves drag them all halfway across the fort and stuff them into a cage which was hooked to a lever, to *force* them to (get killed while trying to) flee custody.
Currently I have 30 or 40 animals in that cage. Gotta get ALL of them stuffed in there before I can safely tame any of them, or I'll wind up with seeds and crap in all my cages again.
[ August 14, 2007: Message edited by: Shadowlord ]