A quick search on here and I couldn't find a reference to underground gaming hit "MineCraft" - is anyone else playing this? http://www.minecraft.net/
It's really very odd - strangely compelling and massively retro in style. I've paid up for it (it's cheap whilst in beta) based on my experience so far.. My initial impression was "crap graphics, meh" but once you start digging (literally as it turns out) you start to "get" the whole thing.
The devs blog is here: http://notch.tumblr.com/
He's sold a lot of copies - enough to start a company believe it or not!