Well, my big and I have stayed in touch since grad. Luckily we both decided to stay in town and work here. We run around in the same group of friends, so it was easy for us to keep in touch. I am actually moving into a one bedroom apt next month, and my big and I are going to be neighbors.
My lil sis is still in school and lives right by the university. It's pretty hard to make our schedules match though. She's all into going out since she has late classes. I have to be at work early in the morning so going out is basically limited to the weekends for me. We set aside time for "family time." We go to dinners and invite everyone in our family so we all get to see each other. This happens once a month or so.
This kinda goes along with a long-distance friendship. It's all about setting aside time to make a phone call or write an email. Granted, you won't be able to see a long distance friend often, but you'll still be able to be close through phonecalls/letters. My bestfriend since I was 14 went away to South Carolina for school, and we actually got closer during that time!