"It's the best film of the year." "They give the performance of the decade." When things are hyped up your feeling about the hype is usually retrospective, in that whether you feel it was justified or not depends solely on whether you agree with it after the fact. Many times you will come across someone saying "Oh it was overhyped too much for me," and that suggests it is because of the hype that you found something negative. That's not actually true though.
What hype does is it frames your reaction, nothing more. You will either like a film/performance or you won't, no amount of hype will persuade you otherwise. You can watch something actively wanting to believe the hype and somehow find you didn't, and vice-versa. All it does is give you an expectation, which is either reached or not, which forms the basis of how you express your reaction.
For example, if you see Liv Ullmann in Face to Face and think it was an excellent performance then hearing people beforehand call it the greatest performance ever captured on camera will not do anything to change that. Same with an overall film like Citizen Kane, which routinely tops best film polls. What it does though is make you say "It's excellent, but not best of all time-good, so I was a little disappointed as it was overhyped" or "it's excellent and it lived up to the hype".
The hype aspect is almost secondary and has no bearing on how you personally react to it. What it does bring is a level of expectation. If you see, say, Carrie because you know it got oscar nominations and then think "My God, what a joke that is," it's not the fact you knew they were oscar nominated which makes you unimpressed - you were always going to be unimpressed, the expectation merely supplements that and makes you express your reaction in those terms.
What hype does do though is legitimise the guilty pleasure. I'm sure many people would have greatly enjoyed Juno whether it got oscar nominated or not. Had it not received all the hype though and not had people going in conditioned to take it seriously as an awards-level film then it may well have remained just a nice little film lots of people liked ... and those unimpressed with it would always be that too, but never use a phrase like "overrated" or "overhyped" in describing the film.
That's the strange thing about hype, it can take a film you enjoyed and make you have negative feelings towards *the reaction* to it rather than the film itself. I've never seen a film and thought afterwards "YES!!! IT LIVED UP TO THE HYPE!!!" When something does reach the level that the hype claimed my reaction invariably is surprise "Wow, it lived up to the hype!" Perhaps that's my natural cynicism coming through though.
Which all means for me there are two camps I can be in tomorrow after seeing The Dark Knight : "Yes, it lives up to the hype," and "No, it's overhyped". I may even like the film a great deal and still think the latter, such is the seemingly meaningless outcome hype inherently has. Whatever my reaction is though will have nothing to do with the hype, I'll either love it, like it, or not. When saying *how much* I like it or not is where the hype will play its role - a role which is a rather redundant, but sadly inevitable one.