I have one on my rigid SS. Works great, more than just taking the edge off. I tend to sit thru rocky sections where I should be standing. On my F29 one, I use a Moots Ti post. The front suspension combined with a long Ti post (and large tires at low air pressures) makes for a comfortable ride.
The 2009 Cannondales are coming thru with such narrow tires, I couldn't comfortably ride them any place rocky.
This is BS btw.. The 09' 29er 1 I just built has Speed King 2.2's that look like 1.85 tires.
NO one is going to be running these in anything but super dry summer conditions. You will also need to run higher pressures to avoid denting the rims.
We will have a bunch of these tires hanging around I bet.