Bikes are generally suited to the person - not the other way around
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I would look for these qualities in a bike, for myself.
700Cx28 Tyres
Drop/Aero Handlebars
Gears
Cyclocross Top Brakes
Generally for commuting a road/touring bike is great, and IMHO much more suited to commuting than a mountain bike frame. I've done both (on a non-suspension'd mountain bike, and my current road bike commuter) and the only thing I like more on the mountain bike are the brakes on the top of the handlebars (which you can do with drop bars with Cyclocross-style brakes).
I've been commuting for 2 years now, and in total have covered ~4000 miles overall (which is nothing compared to most of the guys on here!). The skinny road bike tyres made the biggest different to me, that and the 54-teeth big-ring.