Wrt lipflapping, in live media vids it's called "talky-face" and is generally frowned on, but hard to avoid.

Here's one of mine with very little talky-face, by live action fanvid standards. I think part of the problem is that the people filming the show/movie/whatever tend to point the camera at whoever's talking, and also that fanvidding also often tries to convey emotion, and that often happens when people's faces are moving.

Also, wrt making lips move to the music... in my experience, you can't really do that with live human beings, because we can tell that they're not saying the same words. The motions of a human face when speaking are much more subtle than those of an animated face. I say "in my experience" because I once made this vid with muppets and found it pretty easy to get them to lip sync because, let's face it, when muppets speak their mouths just open and shut... there's no complex lip or tongue movement going on. Lots of people commenting on that muppet vid are amazed at how well the muppets appear to be singing along to the music, because it's really very rare and difficult in live action fandom. (FWIW, the muppets are *really* singing "sailing for adventure on the deep blue sea", but in the vid they are singing "frigging in the rigging 'cause there's fuck all else to do.")

I was talking to lim a while ago and she said that she made "My brilliant idea" (download here) in part as a protest against the "talkyface bad!" meme... she wanted to make a vid with heaps of talkyface in it, but that worked anyway. I think she did a good job of it.