I think if the movie is done right, and is compelling enough, you get so pulled into the movie that you don't notice the time. Of course, if it is going to be longet than 2 hours, they should plan an intermission because at some point your bladder is going to remind you how long you have been sitting there, especially if you get the extra-large soda. I have not yet seen PotC3, nor did I see either LotR3 or KK, but I did endure Titanic and The Right Stuff, and LotR2 and PotC2 were both fairly long as well.
My personal barometer for how compelling a movie is is how much soda I have left over at the end, since on very good movies I forget to drink. Or if I run out, it must not have been that good of a movie, or at least had long dull periods.
I have nothing against long movies, as long as they are compelling enough, and some movies, like the Harry Potter ones, need to be longer just to get the entire plot in. After the initial joy of Seeing Harry Potter come to the screen and being thrilled by the cinematography of it (they were all very pretty), I was disappointed by each and everyone since they were too short. But since the first book was the shortest, and the first movie was around 2 hours (sorry, don't have exact time at my fingertips), I knew I would be disappointed by all of them merely because the stories were too big to fit within the time frame.
I think the movie should be judged not on its time length, but on its content. I liked Piraes 2 because they did take the time to go into the story a bit; I'm sure Pirates 3 did the same thing. I'm sorry if you prefer movies that stick to an alloted time that people are familiar with instead of telling the complete story. And if it is too long to sit through at the cinema, then just wait a month and rent it on DVD. It's not like you have to wait very long anymore.
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