We discuss that alot in the movie thread. I have seen alot of movies I loved that didn't get great reviews. But for the most part I do like to consult the reviews, if they are that low I probably don't check it out. Not unless someone I know (with similar tastes as me) highly recommends it.
I find this especially true of dramas, if they are poorly rated, it is usually for a reason. Comedies on the other hand can be a different matter. You go into alot of them just expecting to be entertained, you know they are not going to win any awards or be life changing. For example I watched Snakes on a Plane twice! lol
And we do care, because there were threads dedicated to what awards Brokeback did and didn't get and how many stars critics gave it, what the reviewers said and so on and so on...