Just thought I'd share my experience...
I studied out of the Official Guide and Kaplan.
On kaplan I got something 640, 620, 640, 560, but I knew better than to be phased by it. I got a 700, and a 720 on the 2 powerprep tests.
Basically, mystudying consisted of doing ALL the questions in the OG. Lots of people tell you to only study the last 50 questions of every section in OG, but I think doing all of them gives you a lot more confidence. Then tackle the Kaplan, already knowing to ignore the final scores (because they seem REALLY meaningless!).
During the exam itself, I was confronted by one or two completely ridiculous problems early on (maybe about 5/6 th question) but barring that there weren't any surprises. At the end of the math, I knew that I'd a get a decent score, it was midway thru the verbal that I realized that this wasn't going too well, and the scores bear me out. - don't forget to practise the verbal guys - just one or two more of those and I would have had a 700!

Still it's better than my last time's score of 640!