Lipsyncing has to be part of the concept of the video.. I've never thrown lipsync into a video because I could (well except in the first version of closer to god because I was young and needed the money

). Some videos can use it, some can't. Often times a video can be seriously hurt by lipsyncing. Some videos rely entirely on lipsyncing (not engel, because that also had stellar editing to back it up). I'll be perfectly honest that videos which are JUST lipsyncing videos I've found to be honestly very lacking. There was this one vid at Fanime called "Teenage anime nurse" which was the most stupid pile of male cow droppings I'd seen in the whole contest (which is sad too because at the very end of their video they have a little thank you to me and my video guides... yet their video looked like crap! How did my guides tell them to make a video like THAT?). It was nothing but a buncha nurse scenes lipsynced to the song - and THAT WAS IT. It was totally un-funny. Shinji's Secret by Ye-Olde Chuck-dogg was kinda funny but in a funny-once sorta way. It actually had a funny concept though.
I think there are some videos where it belongs and some which don't - and the only way to know which is which is to have a feel for the technique. It's an effect like anything else. Some videos don't and
shouldn't have fancy effects (like my Cowboy Blues) just like some videos shouldn't have lipsyncing.
It comes down to the feel and purpose of the video. If lipsyncing can help you achieve the desires emotive response or thematic quality that you're going for, then use it. Otherwise, don't.