Todd Wells won the Pam American Championship, the Sea Otter short track, and at least one other domestic race this year on a 29er.
I now have a couple hundred miles on my Niner Rip 9 in desert and mountain terrain, and have gotten to the point where it feels comfortable. After many years on 26s, and the last 9 years on my 3D Racing custom full suspension rig, it was just weird going to any other bike. Now that is feels like "my bike," my impression is that it climbs as well as my old bike, and the bigger wheels rolling over obstacles helps tremendously on the uphill. It definitely rolls faster on the flats and downhill. It has a very different feel on tight switchbacks, but there have only been a few times I felt that it was a significant hindrance. At first, I occasionally felt the heavier wheels when accelerating from near stop, but it was never a major deal.
One big plus is the thru-axle front fork, which makes steering way more exacting and solid, both on slow technical stuff, and hauling ass. I am sure the 1 1/5" taper to 1 1/8" headtube probably contributes to the solid steering.
I believe the biggest difference in ride is because the hubs are higher than the bottom bracket, as opposed to a 26er where they are about level with the bb. As a big guy (6"5") I am top heavy on a bike, but on my Niner I feel like I am in the bike, as opposed to on top of it. We have miles of fast very twisting single track around Durango, and I now rail turns while sitting down and pedaling that are impossible on my 26er, without standing up and working the bike to prevent the rear end from skidding out. It is an overall more solid feel of the bike being connected to the ground, both when sitting and standing. The bigger tire contact patch of the 29" wheels may have something to do with it too.
I am definitely a convert, and would never consider going back to a 26er. It takes a bigger swath out of the terrain, which has its drawbacks, but the positives definitely outweigh the negatives for me.