SPOILERS CONTAINED WITHIN.
Finally got around to seeing it. (Actually, for me, this is fast.

)
Yes, many changes from the book. I wondered how they were going to frame it, seeing as almost half the book is a flashback as Trumpkin fills in the children on the backstory. They did a pretty good job of reordering that, although I think I had a step up because I had read the book - I'm not sure other people knew precisely what was going on.
One of the biggest changes, of course, was with the battles. In the book, the first battle is discussed briefly in a shortish paragraph. Caspian leads it (Peter et al haven't shown up yet), and it's fought on open country. In the movie, Peter leads an attack on Miraz's castle, and appears to retreat at a random moment - weren't they THIS close to killing Miraz and his ministers? Still, it was an exciting and powerful scene. The second battle was more inline with the book, although much more detailed and longer.
It was interesting changing the personalities of the kids from the book. In the book, Peter's a rather nervous but calm leader, and Susan's the whiny complainer. The movie instead cast Peter as a vain leader, overconfident in his abilities and unable to take the hint, and Susan is a pleasant if rather banal person for Caspian to cast goo-goo eyes at. (Which, in my mind, certainly added nothing to the story.)
Most of the changes worked very well, though. Trumpkin taking the fall for Caspian early on, Aslan not showing up until the end, the expanding of the attempted resurrection, and so forth. And that transformation from train station to cave was brilliant. I may see the movie a second time just to see THAT again.
I'm looking forward to Dawn Treader, myself, because like our ivory-tickling friend here, that's my favorite book as well. And unlike Prince Caspian, it's a straight-forward narrative. A well-written overriding plot with several short "episodes" tying them together. It should need a lot less in the way of rewriting.
Lex