Not to continue too far off topic, but I'd just like to back up the OPs UI lag claims on the original iPad. A large number of original iPad users (myself included) experienced a massive slowdown upgrading from iOS 4 to 5. In dinky tasks like Safari and Mail, my iPad 2 (technically, my wife's) now feels like it is several generations faster than my iPad 1, where before the differences weren't as noticeable.
Anyway, I've tried a few cheapie Logitech webcams plugged into my iPad via Apple's USB adaptor, and none were compatible with it. All gave the "USB device requires more power" message.
If you are considering an iPad 2 for FaceTime use, I can honestly say that the front camera is OK for FaceTime performance. The rear camera takes decent video. But for still shots, both cameras are utter garbage, even in decent lighting.