I'll give my 2 cents - for commuting, I really prefer a mountain bike, with flat bars and a more upright riding position. I know opinions on this vary, but I really did not like riding my trek 412 700c bike in downtown Minneapolis. Even after I put flat bars on it.

I've ridden thousands of miles on drop bars before I ever even rode a mountain bike, so it's not that I'm not comfortable on drops. I guess I just feel more confident if I need to bail out of a situation when I'm riding a mountain bike - jump a curb, ride on the grass or whatever. And commuting, sooner or later, you will need to bail out. There are countless old steel MTB bikes on Craigslist. My commuter is a crappy Bianchi Nyala - I literally pulled it out of the neighbors trash. I have nashbar 1.25" slicks (4000 miles for $10) http://www.nashbar.com/bikes/Product...39_-1___202472 and I just got my christmas present installed:http://www.nashbar.com/bikes/Product...30_-1___202477,

Disk brakes would be nice, but I've got too many wheelsets to justify the switchover. Plus, I subscribe to the KISS principle. Why stick an additional disk on your bike, when you already have one (your rims)?