I live in Mt. Bike Heaven and ride a lot! I rode a Niner Jet 9 Carbon last year, my first 29er - came from a 26" full suspension Tomac cross country rig. I'm 6' tall and ride a size large frame. I generally like it, but there's a few funny things about how it rides and it took me a bunch of rides/time to get used to it. For the trails where I live, and the type of rider I am, the Jet 9 is about perfect in concept.
In general, if you're fit, a 29er can be pretty quick. Momentum is key with the bigger wheels. They shine on middle ring & big ring rolling terrain & the bigger wheels & tires really do provide another inch or 2 worth of suspension.
Like all big expensive equipment purchases, if you can spend a ride or 2 or 3 demoing a few different bikes before you throw down, it's best.
