Single up front, gears at rear

I'd love one to build up one of those, might build one for when i'm back in Ireland, i'm guessing off-road frames with track ends or horizontal dropouts are pretty rare? Chain tensioners spoil the look of SS MTBs for me.

Ahem.
http://www.londonfgss.com/thread11107.html
The Alfine hub comes as a disc brake version. I really like the idea, and have not written off getting one for the singlespeed 29er for extra versitilty. 8 gears which can be changed while the bike is stationary, more resistant to knocks, and weighs around the same as a 3x9 set-up

http://www.chainreactioncycles.com/Models.aspx?PartnerID=79&ModelID=35102
Looks good for a budget hub gear IMHO.