The GRE was incredibly easy. Pretty much simple math and those comparing words problems. There is also a fairly big writing section. It all depends on if you need to take the standard GRE or a subject specific one. But if you aren't used to writing, definately do some practice problems that they provide.
For me, I never studied a single bit for it. My major doesn't require the GRE for grad school however the actual university did. So at the last second, I had to just take it but it didn't matter what I scored. I ended up with a better score than I got on the SAT's so I wouldn't think it's too hard as long as you study. All of the subjects on it are my worse subjects (other than writing) and I still did fairly well unprepared.
.......wow, 30 more days until I leave my job and 35 until I leave for grad school. Where did the time go?