Its weakness, also its strength, is you can't use a belt with derailleurs....a couple of friends have belt drives. Nice clean solution, indeed.
If you think about it, bicycles are far less reliable than cars, despite how much simpler they are. It really shouldn't be so profound in that regard, but if you think back to the time when cars used chain drive (1910s?) instead of shaft drive to move power from the transmission to the wheels, then you realize that the transmission of a bike, exposed to the weather without a lubrication system, won't be reliable.
Now that Sram has the new Eagle system (released last year; I'm not talking about the older Eagle setup) with its proprietary chain and so on, its about the same cost as a Rohloff yet does not have the gear range (although its pretty close). Yes the Rohloff is heavier and less efficient, but if you use belt drive with it you mitigate a lot of the weight issue, and if you are not cleaning and lubricating your Eagle system nearly every time you ride the bike, its efficiency will go down rapidly- at which point the Rohloff with belt drive, which does not require nearly so much attention, is more efficient.