As far as UC's go, Amy's advice would probably hold true for UCLA.
But all the other UCs vary so much in terms of Greek life it's like night and day. Part of it really depends on how "social" the campus is overall. For instance, SB has a great greek system. But the whole campus is known for being "fun". I went to SD. Tiny greek life. But SD is all about studying. Were pretty much known for being an antisocial campus. The student activities office actually had to have a seminar on how to meet people!
And I mean like how to just break the ice w/ a new friend, not how to hook up!
The dedicated an entire day to getting the campus to just say hi to one another.
How sad!