Neil - slightly related - how do you feel about 22" BMX's ?..
Not sure about that one, TBH when you watch BMXers riding big trails they are going very fast and don't seem to have problems on 20 wheels, there's also the added factor that if you build good, smooth trails there really isn't any need for bigger wheels and suspension. With the tricks that are being pulled nowadays speed of turn/agility of a 20 wheel must be a factor.
I have ridden some 24 wheel bikes (cruisers) at the trails and although I did quite like the feeling of stabilty at speed they just felt ever so slightly 'slower' if you know what I mean.
I haven't ridden a 29er offroad but I'm sure it's a similar thing, as pointed out above, it just suits different people's riding styles. I rather like the acceleration and nimbleness of a 26 and am prepared to pay the price in comfort!
1993 Kona Hei Hei, 2013 Mutiny Robbo X-Sekt, 2016 Transition Scout, 1998 Mk 1 Standard Trailboss, 1997 S&M Holmes, 2016 Genesis Tour de Fer, OJD handbuilt MTB, Player Special - 2015 Ted James custom roadie