|The early 2011 iteration|
Mountain style frame: I'm a mountain biker at heart, and I've always been more comfortable with that riding position as a result. It also gets you slightly more upright - it's easier to look around. This bikes' frame is basically a mountain bike frame. This also means it's a little heavier-duty than many road frames.
700c (standard road size) tires: Road tires are generally narrower than mountain tires. To make it really simple - this means you can go faster with less effort on smooth surfaces (such as most roads and paved paths). My tires are a little wider than racing-style tires, but nowhere near what mountain tires would be. NOTE: normally you can't mix a mountain frame and road tires! This bike is designed to do this.
Disc brakes: While I use road tires, my wheels are actually meant for 29" (29er) mountain bikes (29ers used the same diameter wheels as most road wheels - just larger tires). I upgraded to these when one of my previous wheels broke. As part of this, I decided to upgrade to disc brakes. While not essential for commuting, they're nice as they tend to work better in all sorts of weather (and I ride in all sorts of weather).
Seatpost-mounted rack and trunk bag: There are many ways of carrying stuff on a bike. This works for me most of the time - it keeps stuff off my back, the bag mounts quickly and securely to the rack, and the rack can be moved from one bike to another if necessary. Topeak makes what is hands-down the best system for this.
Fenders: You can get by without them, but they're very handy on rainy days (or days when it has recently rained). Mine are made by Portland Design Works and can easily be detached or reattached without any tools. They're also lightweight and fairly inexpensive!
Funky handlebars: Due to a wrist injury several years ago, certain riding positions hurt after as little as a few minutes. These bars are swept back at the ends to allow for less stress on my wrists - and more riding enjoyment! Handlebars are easy to change out in many cases, and can really change your perception of how a bike rides and how comfortable it is. There are a ton of different styles, so it's worth taking a look if your bike just isn't working out for you.
Lights: Lots of them! I run a Planet Bike headlight, a Portland Design Works tail light, and (as of Christmas 2010) a Bikeglow system. If you can't see me, you probably have your eyes closed.
So there you have it - it may not be everyone's ideal commuter, but it works pretty well for me!
Disclaimer: I have not been paid, bribed, threatened, or otherwise encouraged to promote specific products or brands in this post. The opinions expressed are my own and are based on my experience - nothing else! If any of the manufacturers happen to know who I am it's only because I've complained about something...