The most significant differences are that LCD models don't deliver as dark blacks, and some viewers notice rainbow fringes more readily on DLP models.
The DLP technology is somewhat more expensive so just one picture generating element is used for red, green, and blue content and the sequential flashing of the sub-images combined with the viewer's eye movement will always result in the sub-images not coinciding in the viewer's eyes at least some of the time.
LCD's are getting better as technology improves but the crystals are still not perfectly opaque for black, thus you get at best dark gray for your black. The difference between LCD and DLP is more noticeable when the room is really dark.
I haven't noticed but some experts have said that on average the gaps between the illuminated parts of the individual pixels are a bit wider for LCD compared with DLP. If you are sitting really close, you may have seen this "screen door effect".
Video hints:
http://members.aol.com/ajaynejr/video.htm
