Original review (2/8/2011):
This book was intense. It made me feel really uncomfortable. It's hard to put it into words. Definitely not for the weak of heart. Great writing.
ETA 10/31/14 after watching the movie at least 10 times in the last two years:
The movie was a lot more palatable then the book, but still disturbing (at least for mainstream horror). The book and movie are a bit different in the fact that the movie feels more like dark comedy for me, and the book more horror.
I read a lot of horror, and this novel disturbed me and stayed with me even years later. I am debating re-reading it to see if it is as disturbing to me, still.