How much do you research a movie before watching it?

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)?

I read up on a movie on IMDB and Wikipedia. I don't live reading reviews, as they might subconciously force you to have an opinion that you didn't necessarily have before you read it.

I ask my wife if she thinks it will be good.

I watch a trailer and read a small plot synopsis.

I usually don't find out about movies until they're out on DVD, so I'll usually read the back of the box. If I see it in theatres, it's because my fiance has dragged me to see a movie.

Depends on the movie, really. Sometimes I watch a movie not knowing anything about it at all beyond the fact that it's in the top 250 on IMDb. Sometimes I turn on the TV and decide to watch whatever is on. Sometimes I watch multiple trailers. More often than not, these days, I find myself checking the rating at IMDb and perhaps watching a trailer. If the rating is (I'm talking below 6) I generally won't bother with the movie at all, although sometimes a bad movie is so bad it's hilarious, so...

Trailer usually.