Folks at work frequently ask me either (A) why or (B) how I commute by bike.
The answer to question (A) is easy: I enjoy riding my bike. I could very easily (and sometimes do) snag a ride in with my roomie, since my office is on the way to his work/school. I could very easily take the bus (and sometimes do) — TARC has several routes within a couple of blocks from my front door. However, neither of those options gives me an excuse to spend quality time with my bike every single working day (likewise, if I want to be preachy, neither one of them improves my health or greatly reduces my environmental impact, either).
The answer to question (B) is a little more involved.
First, I only live about 4 miles from work. When I tell my co-workers I only live four miles away, they often seem shocked: "You only ride four miles each way?!" I usually just say, "Oh, it's not that long on a good bike," rather than, "Actually, I try to ride at least ten miles a day, so I go out of my way to make my commute longer." I'm pretty sure that latter bit of logic is fairly unique to bike commuters.
The truth is, from a purely physiological perspective, four miles is a reasonably easy ride for any semi-fit person, even one who has spent almost no time on a bike.
I think folks who don't ride tend to use walking as a comparison. For a lot of us, walking four miles would be a big deal — non-cyclists forget that cyclists (except for those of us on fixies!) can glide if they get tired or winded, and that the judicious use of even three gears takes a lot of the pain out of climbing hills. It even takes a lot of the pain out of the Baringer Hill climb — I whine about it, but that's basically because I'm an out-of-shape asthmatic ex-ubermasher who still hasn't figured out which ring/cog combo best suits his native cadence on longish climbs. I used to mash my way through my 15-mile commute, which at least three or four Baringer Hill-equivalents. That was before I got Religion (by which I mean 'cadence' and 'not being a stubborn ass').
Likewise, a lot of non-cyclists have never ridden a well-fitted, well-tuned bike that would be really suitable for commuting. I suspect they're imagining piloting 45-pound single-speed beach cruisers, not 22-pound 21-speed sprint-friendly tourers. You couldn't pay me to ride a 45-pound single-speed beach cruiser in traffic. Well ... okay, that's a bit of a lie. If you paid me enough, and especially if you dared me, I totally would now, as long as you would let me adjust the seat first. A year ago, I would've told you that you were outside yo' mind, then ridden away as fast as my 39-lb Schwinn Avenue would carry me (I didn't know it weighed 39 lbs, back then, to its credit).
Coping with traffic might make a 4-mile ride a bit more challenging, but as long as you have reasonably good bike handling skills and your bike is a good fit, you can develop confidence in traffic pretty quickly. A year ago, I was pretty insecure in traffic. I didn't trust drivers to play by the rules.
Now, I'm extremely comfortable in traffic — more so, in fact, than I am on a populated 'greenway' (an empty greenway, on the other hand, is another story entirely: WOOOO! RACETRACK!!!!). Drivers behave predictably, for the most part, and are protected by 2-ton rollcages; pedestrians behave unpredictably and might as well be naked as jaybirds. I'm fairly relaxed and very quick in traffic; around pedestrians, I'm both anxious and slow. Really slow.
Initially, in the interest of saving time, I would take the shortest possible route — 3.9 miles or so — both ways. I am a stronger and savvier cyclist than I used to be, however, so I no longer look for the quickest way from point A to point B. Even if I'm running late for work, I generally opt for the 4.5 mile route that hooks up with our local MUP (multi-use path), because it bypasses a good number of stoplights that add considerably to the time and effort required to complete my commute by bike.
During my morning commute, the MUP is usually empty; in the evening, I'm not worried about time (after all, riding my bike is how I relax and enjoy myself, so I'm not taking time away from my hobby). The MUP in question is exceptionally well designed — no intersections with cars, period, excepting one juncture in an almost-unused entry to a waterfront parking area for Belle of Louisville staff. I get on and off the path via a couple of commuter parking lots, which neither feed cars into nor cross the path. When I emerge from the lot closest to work, I'm already positioned in a traffic lane, at a stoplight. Someone put some real thought into this thing.
Just like an auto engine, your body has to use more energy to accelerate than it does to maintain a steady pace -- and accelerating rapidly, in traffic, to try to catch the next light while it's still green, can be a real challenge (I'm better at it than I used to be, but part of that is Swift — again, the right bike makes a world of difference). I can maintain a 20 MPH pace easily on the MUP, though it means scanning well ahead for pedestrians, other cyclists, potholes, and so forth (note to self: determine if greenway has speed limit). I rarely encounter any of those things, so I pretty much bypass downtown in around 2.5 - 5 minutes while everyone else is sitting at stoplights.
Likewise, I don't usually ride my commute clad in work clothes, with 10 pounds of stuff strapped to my back (though until recently I was a die-hard Ride-In-Normal-Clothes-ist). I've started carrying lunch for the week (bread, peanut butter, jelly) and a change of clothes in on Monday and out on Friday — my cube has a little closet where I can hang the clothes, and the PB&J require no special storage.
All I really need each day is a fresh undershirt, socks, and underwear — and my tiny inbound commute doesn't get me sweaty enough to require changing those (though I keep spare socks at work, largely in case of rain or puddles). On cool days I wear a grey wool sweater (which, sadly, is now in need of replacement: I'm thinking about sewing it into a more form-fitting bike-dedicated garment).
The sweater keeps me comfortable, doesn't stink (yeay, wool!), and looks good enough to wear at the office (at least it used to; now I just try to find excuses not to lift my arms in hopes that nobody will notice the holes where I snagged it). If it's cool in the morning but warm in the evening, I can stuff the sweater in my backpack and bring it home -- but if it's cool enough to wear the sweater in, it's probably fine to wear it home, too. Wool is awesome.
Basically, the logistics of my commute are surprisingly easy. I plan to write a bit more about this, but I'm out of time for the moment.
The point is that, for me, it's nowhere near as hard as it sounds. I'm neither super-hardcore, nor a superman. I'm just a guy having fun on a bike (okay: sometimes in the rain).