I do that too
It's normally The Stand, The Lord of the Rings, The Outsiders or one of the Harry Potter books for me. And I don't care what anyone says about the Harry Potter books, I'm a big fan

Which reminds me, I'm not sure which Harry Potter movie irritates me more, Goblet of Fire, Order of the Phoenix or Half Blood Prince.
It's not the issue that they don't follow the books as well as other films, I can appreciate creative license, it's that who ever was in charge of the screen play did a terrible job of actually translating the books to movies, It honestly feels like they just didn't care (thinking about it, they probably didn't

as long as they get bums on seats

).
There are scenes that have no business being there, they take up screen time that could be better used to explain the plot.
For example, there's a ten minute scene in Half Blood Prince where Ron's house is burnt down. To this day I have no idea why it's in there, it does not move the plot along, just leaves you asking, what the heck was that?
I'm not saying I could do a better job, but I really think that they could have been filmed differently.
Also as much as I respect Michael Gambon, I really felt he didn't get Dumbledore at all, he didn't play him as well as Richard Harris did IMO.