I think it needs to be said: there are disc brakes and there are disc brakes. What most of you are praising as the be all and end all of braking state of the art are what, Avid or Shimano mechanical discs? Don't get me wrong, they are fine for what they are, but IMO are not worth holding out for. Hydraulic Magura's for a commuter would be overkill, and mechanical discs are definitely more practical than that, but... so are decent V-brakes. Cantilevers. Dual pivot sidepulls. Just saying. On a single (i.e. not a tandem) bicycle, the limiting factor in braking performance is the ~39" wheelbase! That, and the brand of tires you use. My back-up commuter is a bone stock Schwinn World Tourist from back in the day that I found at a garage sale. I am riding it with the original brakes and only recently bought better tires. $12 Kenda's to fit the vintage 27" wheel size. Low tech side-pulls, low tech brake pads, bottom of the line tires. I have absolutely no trouble going on a 8 mi commute through mixed suburban/semi-rural cycling. If you read that as having to use the brakes hard and often at times, on the route, you would be correct. I also have a tandem equipped with Avid BB7's with 160mm rotors. I ride that tandem solo at times so I know how much haul down can be obtained from discs and I know that that much braking power on a regular bike sounds like "oh yeah, bring it on, I'm ready", but, are you really? Chances are the raw power of the disc is limited in the setup and the "advantages" become the wet weather superiority and ability to get away with neglecting out of true rims. Well, discs warp and getting discs absolutely true is a real pain. An expensive pain if you don't know how or don't have the tools to do it yourself. Mostly my bikes (7) have some kind of v-brake and I really think that V's are THE commuter bike brake par exellence. I would absolutely not turn up my nose at a bike just because it didn't have discs.
H