I've worked on lipsync projects before. Thirty seconds of lipsync anims took me about a day to do from scratch. I have much more than that to do, so I can't spend weeks and months working on just the lips, when I got to animate the whole characters too.
I'll go with arcsecond's idea of using lipsync software as a starting point. Of course the software isn't going to get it right in each case, but tweaking and getting a good enough result allows me to spend my time animating the other things used in communication; emotions, gestures, eye focus, etc.
I'm working on a games project, and our time schedules are mean. Other games that have featured lipsync such as 'The Getaway' used automated lipsync software with after-tweaking. I think it makes sense...