In reply to David Hooper:
As above, the slacker angle will make it a bit more sure footed at speed in sweeping runs, but if you like the tight and twisties a more aggressive 70.5 or 71 head angle would be a better choice. However you'll notice a number of manufacturers vary this with frame size too (a small Cannondale scalpel 29r for example has a head angle of 70.5, large is 71.4)
As a by product of the 29 inch wheels the bike will be more stable at a given head angle but slower response to steering input - i.e. a 69.5 on a 26 will be quicker turning than a 69.5 on a 29r in general. this is why some manufacturers (again using Cannondale as an example as I have the book in front of me) have made their 29r frames with different geometries a scalpel 26" medium frame has a head angle of 69.6, the 29r version has a head angle of 71.0.
A month back or so I took out a specialized epic 29r along with a friend how owns a 26" epic and the difference was quite marked in handling. While the 29r was definitely quicker up hills, and climbing and just seemed to roll over bumps better, the steering was slow, and it was much harder to correct your line mid corner if you didn't get it right. This nearly put me off the idea of a 29r as I like a bike you can through around a bit in the technical stuff, but trying a Cannondale 29r the difference in handling was almost gone (the main one remaining was simply that the bigger wheels make the bike rise up on you a bit more - something I can certainly get used to) , but it still had all the benefits of the big wheels and the speed, but more importantly the extra grip it gives you.
I would certainly try out whatever you are thinking about against a few different manufacturers' frames, and look out for those like the Trek and Cannondale (I'm sure their are others too) that haven't just taken a 26" frame and made it big enough to take 29" wheels. (Orange may well have not done this, perhaps their 26r has a head of 67 ish - but it does seem quite slack)
I'm still looking for my next bike (I want am XC specific short travel full sus) and haven't made up my mind fully yet, but highest on my list are the Scalpel and the Trek Superfly 100, I still have a few more to try... at least the sales don't start until August!