I studied a fair amount, especially on the math—it's been 5 years since I've taken a math class, so studying there really helped. ("fair amount"= probably 4 hrs a week for 2.5 months)
My studying was structured around a Kaplan class I took, which I would really strongly recommend against. It's very expensive, and I found it frustrating to not be able to move at my own pace. Most of all, though, I think Kaplan's materials are quite bad, especially their verbal. Their more difficult text completion questions are just hard in a different way than ETS's: Kaplan makes text completion hard by using pretty obscure words. I didn't encounter any words I felt like I had never seen before on the GRE or in ETS's official practice tests. Instead, they make text completion hard via convoluted sentence structures and sometimes making it impossible to predict the correct answer for any of the blanks without looking at some of the answer choices, and seeing which together would make the sentence make sense.
Magoosh has GRE book reviews.
