Oh, yes -- I read reviews. Lots of them.
Usually, reviews often tell me things that say a gameplay video or a trailer can't tell me -- such as, if the game right out the box has any game-design issues, if the game has bugs, if the game has performance issues, if the game has any technical issues -- things of that nature. Usually, that's my biggest concern in a review.
Also, I find it important to know how long/short a game is; usually reviews tell you this. If a game's short and doesn't have much replay value, I'll just wait for a price drop.
I also find it important to try game demos and look at a game's Tech Boards, too. If there's nasty issues on certain hardware I own or if it's laced w/ a certain protection scheme I don't like (i.e. StarForce or Securom Internet Edition), I'm likely going to holding off for a while.