Is it true you can raise your GRE score by taking prep courses beforehand?

Some places claim the average person taking their prep courses increase their scores by an average of 200 points

Anyone want to share their experiences with GRE prep courses?

I’m looking into taking a GRE prep course, but would like to hear from people. Good, bad? Kaplan, Princeton Review, other? Private tutoring, online tutoring, alternate methods?

Did you find their methods helpful? Bad? Did you get your money’s worth? Did you get the refund they promise if you don’t raise your scores?

I am looking EXPERIENCES about the prep courses. I know a lot of people just say study from the books, there are online things, etc. but I’m trying to gather as much information as possible.

What types of GRE prep courses would you recommend?

GRE online prep courses, in-class prep courses, etc. and by who? (kaplan, princeton review, etc…)
What was your experience with the prep course you took?
By who and and what type (online or in-class, private tutor)?

Which GRE prep courses are considered the best, and the worst?

I would love top hear personal experiences with some of the more popular (and unpopular) prep courses, like Princeton Review, Kaplan or Testmasters. Also, has anyone heard of MILC? They guarantee a score of at least 1300 on the GRE. Any input on this would be greatly appreciated. Thanks!