[shiroiushi]

From what I've read about the well-known commercial ones (namely Rohloff), basically the tradeoff seems to be that they're very reliable (thanks to the enclosed, sealed design), and have the nice feature of being able to change gears when not moving, in exchange for greater weight, a more limited gear ratio range, a little less efficiency, and a much greater cost.

[iggldiggl]

Rohloff (or similar ones) is the luxury model if you really want the same gear ratio range as a derailleur gear, but with a hub gear, or respectively the maximum possible efficiency possible with a hub gear.

For regular everyday city biking something like a Shimano hub gear still works well enough, and much more reasonably priced. You lose some gear ratio range and a bit of efficiency, but it's still very reliable.