I migrated my single player world (dating back to Beta 1.8) to a server so some of my coworkers at the time could play too. It's not really huge, but I am strangely emotionally attached to it. My server was down for a few months (and I wasn't playing at the time), but I recently brought it back online. Minecraft seems like one of those games that I'll play forever, like Super Mario Bros.

http://minecraft.cgore.com