Graduated in 2008
Have my core group (5-10) that I talk to and see on a very regular basis, and hopefully we'll be friends for life.
Have another group (15-20) that I will see for special occaisions (birthdays, etc) but don't will not see them more than once or twice a month, although it is always good to catch up with them, I somewhat expect to slowly drift away from a lot of them, but there are a few in this group who I will always try and keep in touch with.
Then there are a few others who since school I have become tighter with through uni or others friends. I generally don't keep in contact actively with these people, and when our current relations end (eg graduate from uni) I probably won't see much at all.
The rest....stuff them, wasn't friends with them in high school for a reason.
If the school had a reunion in a few years I'd probably go, if for nothing else than to see the people in the second group.