Why you want or need a 26" wheel is to put on the back of your bike to keep the wheelbase short and the handling snappy. Seriously, most of the handling benefits of the 29er wheel happen at the front.
I have ridden 26ers for 20 years+ and I went to a 29er a couple of years ago. When I got the opportunity to try the Trek 69er I went for it and the ride is unique. More fun than I have had on a bike in a long time. This bike loves to wheelie drop, manual and pop the front over logpiles, roots and rocks etc. It descends like it's endo proof.
The Fox fork is propietary to Trek and Gary Fisher, having a reduced trail that keeps handling quick at low speeds.
First Trek I have ever got excited about. Everyone else that I know of who has this bike is just as enthusiastic about it as me.