A good movie according to a bunch of other movie goers. If we did the same thing here on KMC, and most everyone thinks POTC is a good movie, would you believe it, or would you take into consideration everyone's predisposition to liking anything their favorite actor or actress is in?
Besides, "United 93" is more than likely getting sympathy votes from people who didn't even see it, as well as negative votes for people who are against it as well.
So, in closing, IMDB is nothing by which to grade a movie's worth, IMO.