My ex was a Delta Sig, and he got me more involved again as an alum (because he really was), so that was really cool.. but now, I find people that weren't Greek in college think it's weird that I'm still involved as an alum.. they just don't get it.
For me, it's a chance to get together with new people, and do quite a bit of community service again.
I think that last one is the only time I've actually dated a Greek since college.. and then it was pretty much Sigma Chi's and one LXA.