I assume everyone knows what Minecraft is, unless you just came back from 3 years journey from Mars.
Personally I don't play it, but noticed how vast the worlds are, how many events occur, and how terribly slow the current server implementation is.
So I was thinking, it would be a nice showcase for our technologies - especially fast clustered messaging (HornetQ) and cache (Infinispan).
Perhaps a keynote demo for the next year :-)