Rarely / Never
I used to run quite a large MMO Minecraft Server. It had Races, Classes, Talent Trees, Quests, NPCs and more. We even custom made the world, which was awesome. However, going from that, to building a mud hut just isn't the same, and most of my friends don't play anymore.
I might do an Adventure Map once or twice a year with my housemates, but that's about it. Minecraft is a great game, really is, but it gets to a point where it loses a lot of value for me.