Main problems with disc brakes on a commuter :
- They make noise
- The discs are easily bent (although it's relatively easy to correct)
- They're not that easy to work with
That's what I gather from people who bought bikes at our shop.
To me, the best design is a drum brake (Shimano RollerBrake or SRAM i-brake) which has excellent braking power in the wet, requires less maintenance and make no noise.