Personally: The Princeton Review Prep Class... didn't help. I also spent over 8 months preparing for a test that I knew from the outset was not ever going to be an accurate reflection of my abilities.
The Princeton Review does one major thing, and a couple of minor things. The major thing is it forces you to study. I took a condensed course over the summer... twice a week, three hours a night, probably 20-25 hours a week of studying outside of that. I was working full time at the time, but not taking any classes. For the vocab prep, I read vocab words into a mic, made mp3s of them, put them on my iPod, and bored the hell out of myself every day during my commutes.
The minor things are basics that you may have forgotten. Special triangles, process of elimination, word roots, stuff like that. Also, it teaches you the importance of getting the early questions right, because of the computer adaptive system.
I took the GREs three times, twice under the old system (paper, V/Q/A), and once over the summer (computerized, V/Q/W). My scores on the old tests were lackluster... taking the best sections, I almost, but didn't, crack 2000 combined. With the new one, low 700s for both and a 5.5. Meaning, good enough to keep me out of auto-reject for GRE scores for everywhere I'm applying.
The other thing is, Princeton Review seems to be more geared to raising the scores of the middle-candidates. It won't raise you from a 700 to an 800. It may help you get from a 650 to a 700, it may be best at getting someone from a 550 to a 620 in a section.
All that said, I still think the GRE is a crappy test, predictive of nothing. Same with the GMAT. LSAT actually has some predictive value, and the MCAT tests knowledge of science, so that's something legit.
On the whole, I think the GRE is trying to get at how likely a person is to succeed in grad school. Which it doesn't seem to do. It's like trying to extrapolate how well someone will drive an 18 wheeler based on how well they do on a written driving permit test for passenger cars.
