I believe he uses a Das at work(saw it mentioned in a story about Mojang a while ago) but he mentioned on stream that he's currently using an old IBM Model M.
Both are nice mechanical keyboards with a wonderful sound though :)
Is there a reason why one would prefer a Das keyboard over a Model M?
Native USB, choice of switches, appearance, full NKRO. I would be fine with a Model M myself, but those are at least a couple distinct differences.