I generally dislike them, but there are a few that I've liked. However, they all get old eventually. I'm not particulairly keen on the GIF format regardless of whether or not they are animated anyway. The all-or-nothing approach to opacity/transparency makes the feature almost completely useless, and loading animated GIFs from a server that's under heavy load makes them ugly and annoying.
That's just my opinion, though. You'll no doubt find plenty of people that think that the GIF format is better than sex.