I've worn one out so I'm more qualified than most here, and I have to give it the thumbs down. I'm exactly the sort of person who should have one: a winter commuter with an expensive but low-performance bike. With the Alfine eight speed (awesome hub), hydraulic disks, dyno lighting, studded winter tires, fenders, and a basket it should be as reliable and practical as my motorcycle, right? Just hop on and go anytime!
Next to the brakes, the centertrack belt has been the most troublesome component. They take quite a bit of pre-tension and getting it right is a big pain. I think the tension killed my BB bearings. It squeaked quite a bit; graphite powder helped sometimes but lubricating a belt misses the point. It's aluminium chainwheel wore out first, well before the belt and cog. LBS says they don't last as long in snow and mud but that also misses the point. Last year I switched to BMX chain and paraffin wax, haven't looked back. For my next bike I'll look into a Dutch style full chaincase, but I'm sure that comes with issues of its own.
The only application I would use it in is fixie. Not a fixiefag myself, but I suspect that the zero back-lash and slight 'rubbery' feel would give a very pleasant feeling of connection to the road.