I agree that it depends on the school. At U of Georgia, I had some friends who were in a sorority and their activities all sounded fun and worthwhile. At the U of Oklahoma, however, the frat and sorority people really try to set themselves apart from the rest of the students. There is a clear line between who's in one and who's not, and there is a lot of hatred on both sides. I've also heard the horror stories from people who were greek, boys and girls, and I dated a guy who was hardcore Alpha Sigma Phi. Dating him, I learned way more than I ever wanted to about frat life. Pretty unsavory, bad for your grades, and priorities in the wrong place.
I know they try to do lots of good volunteer work, but I attended a Heart Association Walk for my company, and there were several greek organizations there. They were all gone from the walk about five minutes after it started (it lasted about an hour). Just came to get their participation points. I laughed my ass off when the student paper ran a story about the frats and sororities "participating" in the walk. At OU, I would say that greek life is definitely not for me. GDI all the way, to this day!