My big and I have stayed pretty close, especially since we've been out of school a long time now and live three hours apart. We didn't pick each other originally, but I think it wound up being a good match.
I have three littles, two of whom I was very close to in school and who I do stay in contact with, but mostly by email. My third little I took my senior year and that was a mistake. I was too caught up in graduating and getting into grad school to be really involved.
My big sis is awesome, we just reconnected a couple of years ago, and we partied like (aging) rock stars last homecoming!