Since my LS and I were the first undergraduate line at our school/in our area, our big sisters were mainly the graduate chapter sorors who worked to bring us in, and I have kept up with many of them, including our former grad advisor. I had been keeping up with our DP until I moved to Chicago, and I recently heard she's ill and living an ATL area care facility.
Of the sorors we made, I am etremely close to the first line we took over (know where all four are, what they're doing, been to weddings, graduations, etc.). All but one was either in or at my wedding and I've seen all four in the last 12-18 months. Of later lines, I've kept in touch with two other sorors, and the other four sorors made by our interest group, well, let's just say they weren't studying keeping in touch!