I am not a fan of movie trailers, I think they spoil way too much of the movie most of the time, and if they don't spoil the movie then they are often misleading. I admit I will watch them for movies I know nothing about, but for movies that I pretty much know what it will be about I avoid them like the plague and I think it has caused me to enjoy movies more.
A perfect example of why I hate movie trailers is Terminator 2 If you watch the movie you see it is set up to look like Arnold is the bad guy, which would make sense to anyone who watched the first Terminator. It isn't revealed until the two Terminators meet, that Arnold is the good guy. But thanks to movie trailers I already knew who the good guy was it and it seem to steal some of the fun out of the movie.
To me, watching movie trailers is like skipping chapters in a book, where is the fun in that?