my two cents
a lot of great info from everyone. I thought I'd throw in my two cents.
This year I went from 26" to 29", and I won't look back. Being on the taller side (6'), the bigger wheels just seem more proportional.
I'm a bit of a data junky, and before buying a 29er, I demo'd/tested several bikes and did some "time trial testing" on my favorite loop. If I maintained the same level of effort, I was faster on the 29er. For a 17 mile loop, I was about 4 minutes faster on the 29er (I think, I'd have to look back to verify, but I know it was significant). Each ride I did my best to maintain consistent effort (based on HR) and similar conditions. The rides were only a week apart, so my fitness didn't change much.
I think each bike is a tool for a different job, but overall I believe the 29er hard tail is the best for me.
In the end I decided to get a cannondale carbon flash 29er. I love this bike. it begs to be in the big ring and go. Maybe it's all mental, I don't know...