I agree that weight really doesn't matter. Once you strap everything onto the bike (rack, panniers, lights, water, etc) the bike will end up in the 40+ pound area.

The weight doesn't make that much of a difference on my commute - it takes me between 43 and 46 minutes each way, every day with about 4-5 minutes of that time sitting at traffic lights. That time remains constant regardless of bike (based on my 40+ lb commuter and my 22 lb road bike) because of the lights, but I get a better workout on the heavier bike.

As for disks: if you are going to be riding all year round, I highly recommend disks. Better/more consistent braking and less wear on your rims = all good.