Ok I was in a frat 3 of my 4 years in school and while it hurt my grades a bit (always someone to go out with so it was my fault) it was over all a positive experience.
First off ignore the people saying you pay for your friends and the like. That’s bullshit. Its a typical answer from someone on the outside looking in. Frats are exclusive by nature and that makes people jealous and bitter. Money was the least concern in joining a frat, hell it cost the same to live in house with food as the dorm, and no one was getting rich off it.
Know that different frats are NOT alike, they are very different. Some will be the jock types, the pretty boy types, the stoners, the geeks etc. This is because frats tend to select for people that will fit in with the group. Its not so much elitist, just who wants to hang out with who. A frat with a lot of good students isn't going to get along with a pot head who is selling his books for weed, so the pot head won't be asked to join. Its important you find a frat with the kind of people you want to hang out with. There will be diversity in there, you are not all carbon copies but lets be real, some people don’t' play well together.
What a frat gives you is a group of guys much like yourself, in a common location, and a set of traditions and actives which help build friendships.
Socially the parties tend to be great, and its amazing the kind of things you can do with 50 guys working on set up. My favorite of the year was a party we had with a couple of hot tubs, about 10 tons of sand, two teeky heads we turned into a pair of waterfalls flowing down the side stairwells, and various other touches that made it quite different then the normal sausage fest apartment party in college.
Now academically I suffered a small amount but that was my laziness. I took pride on having a good GPA while almost never attending anything but the exams. It was stupid but I was young

. On the other hand I had quite a few friends getting all A averages, in very difficult majors, so academically you can still succeed if you are willing to work, just like being anywhere else. Most Universities have a ranking for frat GPA's, you can check that out if you are worried about slipping academically.
Most importantly I met a girl, freshman, in a hot tub, who I later married and have been with for 13 years now. Glad I was at that frat party
