Do 29 inch wheels make a difference?
Since I switched to my 29-er in september, I can keep up with the fastest bikers in my "team". Before that I just could not. It could be due to the new material, but I think there's a speed difference of about 2 km/h.

I bike on the flat tracks of nothern Belgium and the south of the Netherlands. So no climbing or descending.

The 29-er is definitly faster on (loose) sand, and mud. And a lot more comfortable on tree-roots and the "Belgian Blocks".

For really, really small turns, I notice the wheelbase is larger, but otherwise I do not notice any difference in handling.