For Rev4:
The Pro league is for bencher's who are sponsored, or who just want to be in the pro league. There are 37 folks in there atm.
The xtreme overclockers league is for those who use sub-zero cooling and are not sponsored (i.e. buy their own stuff, lol). There are 2,312 of those peeps atm.
The enthusiast league is for those bencher's who only use air or water cooling...pic required. Once you submit one sub-zero entry, you're kicked up to the xoc league. There are 14,696 members atm.
All leagues compete for the same pool of points though. So if you are beat by someone in a different league, you will loose points, and possibly ranking within your own league.
They opened up points in a few more benchmarks (3dm11, pcmark's, etc), and now give full points for all single and multiple gpu configurations.
The site is kind of bare bones right now as search functions, notifications, etc. leave a lot to be desired. no sigs either, so those are frozen in time as far as where you were in Rev3.