Not singlespeed 29er but...
Rohloff on I-Horse MKIII
Over 1.5 years of year-round riding and this bikes gets about 80% of my ride time. I'd, personally, never go back to derailers on a trail bike. Those things are for roadbikes only IMO. The Rohloff has a niche' it fits in (trail riding / Downhill, perhaps) and it does a great job at it but it's not the best tool for every job out there.
-You'll add about 1 to 1.5lbs to your bike compared with a derailer system
-The weight will be redistributed on your bike, making it heavier in the rear. I've found this to be nice for wheelie drops and such but a bit of a challenge in getting the rear very high on a bunny hop.
-Built into the wheel so if you're hard on wheels, you better learn to build them yourself or be ready to spend your pennies on the local builder.
-Doesn't shift all that well when the temps get super cold ("super cold" being a technical term)
I've only ever experienced this once,and while noticeable, it wasn't a huge issue.
-Shifts without pedalling
-Shifts as many gears as you'd (1-14) like in one simple motion
-Hit your shifts EVERY time with no hassle
-Ease of maintenance (after over 1.5 years, only one oil change to date). The chain, itself, is now my biggest drivetrain maintenance item.
-Less vulnerable to trail obstacles. (I bent a derailer hanger and the hub still shifter perfectly. I didn't even notice it 'til I got home and saw the chain tensioner at a crazy angle)
I'm not going to put a Rohloff on my light-weight road bike but for the trail, there's no looking back for me. The weight penalty is a small price to pay IMO and becomes a non-issue after only a couple rides. Your conditioning will accomodate the change in short order. All my friends ride derailers and I seem to be able to keep up in groups without issue. The cost, on the other hand, is something every potential Rohloff buyer will need to wrestle with on their own...