Anyone who is worried that the children will be too old to play their parts need to keep in mind that there are strong rumors that book 6 will be released in June of 2005, meaning there will only be on more book left to write, and need to also remember a network called WB where 20-30 year olds often play high school students, and lets not forget the show that started it all...90210.
Also, POA nearly beat the Finding Nemo record for most DVD sells in one day, so even if the interests in the movies are waning, they still make much more money than the average movie.
I also think that some people are forgetting an important factor that contributed to POA making less money than the other two (although it's really not that much less and was WB's most money making movie of the year). POA opened during the summer, a big time for money making movies with huge budgets in advertisements while the first two opened around Thanksgiving where the competition isn't as stiff (I mean just look around right now).
I think POA did very well considering it opened between the record-breaking Shrek 2 and the record-breaking Spiderman 2.
I'm also of the opinion that Prisoner of Azkaban was an excellent adaptation of the books, and that Cuaron got what JK Rowling's world was all about.
"I've got to get me out of here
This place is full of dirty old men
And the navigators and their mappy maps
And moldy heads and pissing on sugar cubes
While you stare at your books."