How much do you research a movie before watching it?

[blackmage_nuke]

How much do you like to know about a movie before watching it?
Read the imdb summary?
Watch the trailer?
Read reviews?
Just look at the poster?
Just look at the title?
Blindly pick movies at random?

Personally I like to know as LITTLE as possible before watching a movie. If its a director/writer who has yet to disapoint me (eg Christopher Nolan), I try to block myself as to anything about what it could be about, sometimes I dont even know the genre when going to see it. I deffinitely dont like to watch trailers unless it's a movie Im not sure about. When it comes to watching older movies I'll tend to VERY lightly skim the imdb description and look at the movie poster.
Sometimes I end up expecting a comedy and end up watching something dark and serious. For example, Barton Fink: it had John Goodman on the poster and there was a reference to it in Monkey Island 2 and with my quick skim of the description it sounded like a light hearted fish out of water story.
But what I really love is when Im expecting something serious that ends up to be an unexpected source of chuckles. For example Hanna, which I knew nothing about since it was just what my friends wanted to see at the movies at the time and what I thought would be an action movie that took itself too seriously turned out to have quite a few light hearted laughs in the middle.
Then there are the movies that take me completely by surprise, like Fight club which I thought was just going to be like another Rocky movie, or Gangs of New York which I expected to be like the Godfather or maybe like Scarface.

SO two topics, how much do you research a movie before watching it and what movies have turned out completely different than what you expected (for better or for worse)?