My take on it after two weeks and 200 miles on a rigid Scandal. Ridden all sorts of terrain - local woods, long rides on easy trails (railway paths and towpaths), Rothiemurchus and Glen Feshie, Glentress, Pentlands, bit of commuting.
Very impressed with it - it's far more useable than a rigid 26er would be, and in swoopy open stuff it's a hoot, but certainly wouldn't want it as an only bike.
Pros
Roll smoother and faster over holes and bumps - yes, definitely. Less upset by braking bumps, smallish holes and square edges. Seriously impressed with how much a rigid bike can handle
More traction from more tyre on the ground - maybe, but I think the bigger wheels rolling over stuff has more to do with it than contact patch. Have ridden up some loose steep stuff and steps I normally wouldn't make on a 26er, and it can take smooth, sweeping corners well quick
More rolling momentum at speed think so - seems to carry speed a bit better (or rather feels like it looses speed a bit less easily than a 26er if that is different)
More stability due to longer wheelbase and lower CoG - certainly feels stable and much more "in" the bike than 26ers which IMO is good thing as long as you keep pedal clearance
Proportionate wheel size to body height helps taller riders get better bike fit - I'm 5' 11" and riding an 18 frame so not sure I can comment here cos they don't make 29ers much smaller than that
Cons
Larger wheels create more drag and less lively ride - not hugely noticable - suspect rigid ride "involvement" is offset by any negatives here
Harder to accelerate - Yes - first couple of pedal strokes seem a bit more laboured getting up to speed, but once you're going you're in business, and carrying speed means less acceleration anyway
Harder to manual wheelie because of higher axles - Very noticeable, but possibly doesn't matter as much as rolls over things better and more "in" the bike so less teetering over normal sized drops etc
Slightly slower turning ability - Sweeping turns and berms are ace , but slow speed stuff is a more of a challenge - need to "flick" the bike into turns a lot more. The turning circle is a bit larger too; there's one trail junction I ride that I basically have to do almost a complete turn back on myself to get into and i can do that on 26er but have to hop the back wheel round a bit on 29er - it just don't fit.
Heavier than comparable 26er - Can't really say. 29er is lightest MTB - probably because it's fully rigid - don't think much in it