I have what seems like billions of pond snails from several water wisteria plants I purchased from my LFS. I am not a fan anymore...but they're alive, and I don't want to kill them... :P
I tried "starving" them, but even when I only feed enough for my bettas, they just attack my plants and eat those instead...which I'm irritated about, since I was hoping to have a good stand of water wisteria by now...but the snails keep eating it. Argh! ;)
So far, they haven't harmed my bio filter/caused any spikes, but I have been told by several people that they will probably clog up and kill my actual filter. I have found several *in* the filter thus far.
Since I can't bring myself to kill them, I believe I'm going to round them up with the lettuce method and deposit them in the lake where a friend of mine lives. From what I have read online, they should be fine in the shallower portions of the lake (as in where Melissa has her dock).
I do like the fact that they're definitely keeping my tanks really clean...but since I do weekly water changes *anyway* in filtered tanks...this is really a non-issue. I think once I can get rid of these buggers, I'll be purchasing a mystery snail (or another slow breeding/non-self-breeding type) to clean up anything, but to prevent this snail infestation I've currently got going.
As for quarantining the plants, you can also use saltwater. That'll kill any snails that might be hanging on, and won't harm the plants.