I see this as the best option for the UK's man-made trails and our changed-weather.
Ti, and blast-graphics, obviously!
Thinking of the Meridas, MM, SITS, Click24, SPAM and other "endurance" type events, rather than tight single track, which, whilst being many a riders' Mecca for riding bikes, is, in the real world that I seem to ride through, actually only a small fraction of what I ride weekly / monthly.
I'd already have one except I'm not a big fan of concentrating the weight of the bike at the back axle from the point of view of handling/unsprung weight. If there was a BB driven version/GBoxx version around the place I'd be very interested indeed.
The Nicolai full suspension G-Boxx bikes show a lot of potential, but their smallest travel GBoxx bike is still too 'big' for my tastes with 167mm rear travel... I'm barely hitting the limits of my Trance with 110mm travel.
Nicolai have been threatening to bring out more GBoxx bikes for quite a while though, nothing new on the website since I last looked circa 2006...
The sooner the better ... A hardtail with a GBoxx bolted into the frame (Forming a structural part of the frame to keep overall weight down) and vertical dropouts (Chain tensioner should be at the GBoxx) to either a fixie hub with a disk or a freewheeling hub (Should be better in mud as the chain won't continue feeding crap from the tyre into the sprockets while you freewheel) to give easy wheel removal and disk alignment and a really light back end with nothing dangling off it sounds like the perfect bike for most of the year here (While it's dry it doesn't matter what you use )...
I'm in agreement that the Rohloff hub is a good idea but that it does give the bike a rearward weight bias. How much that would affect your ride is debatable but I've been waiting (pardon the pun) for the weight to come down before going that route.
I'm a big fan of the 29er thing though and that On-One is a very good price (and gets great reviews).
That may be the last hardtail you'll ever need to buy if you build it up. My riding style involves a lot of serious weight shifting, as well as picking and placing the wheels on really tight trails. I reckon the rohloff would make the back wheel harder to pick up (With flat pedals - I use SPD's sometimes too, but I'd hate to have to), as well as making it more likely to hook up on square edges while you're rolling...
The other thing that puts me off Rohloff hubs is that AFAIK the pickup on them is quite poor (Lots of pedal turning before the freewheel picks up and you get forward drive). Given that the 16 point engagement on the XTR on my current hardtail is painful to use at times (Trials bike has 72 engagements, full suspension has 120, so I know what proper pickup is in a freewheel), I'd be slow to go to anything with a slower pickup than that because it leads to stalling on really dodgy stuff where I want to put power down very precisely.
Incidentally new Shimano XTR/XT hubs have 36 points, but based on a friend of mine and I both snapping XTR axles after less than a year's use, they're a waste of time. Hollow thin-walled aluminium axles with threads cut into their outside surface are a pretty stupid idea from a fatigue resistance point of view...
... A hardtail with a GBoxx bolted into the frame (Forming a structural part of the frame to keep overall weight down) and vertical dropouts (Chain tensioner should be at the GBoxx) to either a fixie hub with a disk or a freewheeling hub (Should be better in mud as the chain won't continue feeding crap from the tyre into the sprockets while you freewheel) to give easy wheel removal and disk alignment and a really light back end with nothing dangling off it sounds like the perfect bike for most of the year here (While it's dry it doesn't matter what you use 
)...
