[kvs]

Looks like there needs to be some data engineering to be done to back memory up with disk storage. I think you guys, by now, have enough information about users and checkins to create algorithms that can determine "hot" checkins vs. "cold" checkins as and when they come in. Because not every user is the same, a more user-centric view can definitely help you come up with a more scalable (or graciously failing) system. For example, I don't checkin as much as some of my friends who checkin 10-15 times a day. So, there is no point in giving my checkins as much priority as those busy folks.