A friend of mine studying using books and did quite well (upper 600s). However, his big complaint was that he didn't feel comfortable taking the test on the computer. It is a SIGNIFICANT difference in taking the test on computer vs in a book. He ended up buying online study/test guides and scored much higher.
I think I qualify... used only Manhattan GMAT and OG books, took the test once, scored 770.
I do think though that I had a solid background before even touching the GMAT. I sat in trial classes and found myself being bored at least half the time while waiting for other people to understand things.