I can't say one way or another if you should do lyric sync but if you decide to do it here are two very common problems with it that you might want to avoid:
1) Make sure someone can understand the song. Any song where the singer mumbles, the music overpowers the singer, is in a foreign language, has a horrible accent, or is in any other way difficult to understand then do not lyric sync. Basically if you had to listen to the song more than once, or worse yet pull out the lyric sheet, to figure out the lyrics then don't sync to it. Nirvana, for example, is generally hard to understand the first time you hear it and probably is not suitable to lyric sync.
2) Don't include an out of character clip just to do lyric sync. For example, if you're doing a dark depressing drama but stuck in a Love Hina boobie grab because of lyric sync then you have a problem. The overall tone of the video is almost always more important than any specific lyric sync, I'd rather see no lyric sync at all than out of mood scenes lyric synced. I'd suggest watching the final video without sound to pick out if you inserted this type of inappropriate scene easier. Not all cases will be as blatently wrong as my example so pay close attention to the overall feel of the video and don't hesitate to strike out anything that deviates from that.
If your curious, <a href="
http://www.animemusicvideos.org/members ... 0558">this video</a> shows why you shouldn't violate the first thing. The lyrics are either japanese or heavily accented english so most viewers just won't catch the sync. <a href="
http://www.animemusicvideos.org/members ... 5256">This one</a> shows the importance of the second issue, it includes several semi-humorous clips when the overall tone isn't humor. Note, both examples are my own creations because I'm not going to insult another creator by publicly pointing out their vids as negative examples.