Has anyone else tried this yet?
Http://minecraft.net
I've been aware of it's existence for a little while now due to various blogs and podcasts but have only just tried it myself.
It's rather hard to describe but is basically a sandbox world where you have to create everything yourself from raw materials lying around the place.
It looks like a 3D adventure from the early 90's but don't get hooked up on the graphics, it's bloody brilliant!
When you first start you won't have a clue what to do but go and search for a YouTube video called your first day tutorial (or something like that) which will help immensely.
Enjoy!
Dave