Bigyinn: You genuinely get 29er rollability without buying very much at all. Also it's just different and fun to play with.
I've owned a 29er Singular Swift which was great – sold to fund another project but I'd have it back. Found it was for non-technical stuff, wonderful on long days out over the hills. The 69er gives you (well, me) a nice compromise.
Best 69er I tried was the Singular Hummingbird at SSUK 09. Borrowed it pissed on the Sat evening, found the little pump track near the campsite and had a ball. Passed it round all our party who all loved it.
The 4569er above was close to as good, and I'm looking forward to giving the Inbred 69er build a proper hammering. 10 mins round the local woods so far and it seems good. Big tyre in the post from CRC. (That's a 29er 2.1" Vapor on there just now).
al.
EDIT: Here's that Hummingbird 69er
http://www.flickr.com/photos/singularcycles/2728899823/