If you haven't tried riding to work yet, or you just want to convince the folks on your weekend ride to make the attempt, we have the answers:

Excuse #1: Are you crazy?
OK, riding on the street's a little scary at first, but so was kissing-it just takes some getting used to, so you might want to try it first with a friend. Soon you'll figure out the safe routes and develop the protective instincts. The SFBC has maps and safety handbooks to help. Download the PDF: Safe Bicycling in San Francisco.

Excuse #2: Commuting's for granola-burning geeks with mirrors on their glasses.
Tell that to the messenger with the five facial piercings doing 35 down Nob Hill with no brakes. And those guys basically bike-commute for a living. So no, it's not geeky getting a ride in every weekday, rain or shine; it's 'core!

Excuse #3: I haven't got a thing to wear.
Contrary to popular belief, high-end bike saddles can indeed come in contact with textiles besides Lycra without voiding the warranty. With a few nips and tucks, you can ride perfectly well in your work wear. Or keep nice shoes and clothes in the office, ride in race garb, and change at work. Or compromise with looser-fitting, multi-purpose mountain-biker-style wear.

Excuse #4: Fenders would emasculate my bike.
Au contraire, my streaky-backed friend. First of all, big-fendered downhill bikes are the ultimate in mountain-bike extremeness. And a pair of full fenders lends class to even the most mass-market road bike. Besides, when the spring rain ends, your machine can resume its svelte, bare-tired silhouette for the long, fast rides of summer. Useful-ize your steed!

Excuse #5: Well anyway, I'm not subjecting my baby to the mean streets!
OK then, here's your excuse to buy another bike, Mr. or Ms. Gearhead. Hybrid, touring, or cyclocross bikes make great commuters; they're sturdy, comfortable, and made for fenders and racks. Same with old rigid-forked mountain bikes and vintage ten-speeds (plus, they're cheap, and you can upgrade parts for an elegant retro ride or bitchin' single-speed).

Excuse #6: I don't have time.
Please. If you live in the city, by the time you've parked or waited for Muni, biking's either faster, or it's a wash. For the thrill of competition, time your motorized commute and try to beat it. In any case, riding's riding, so you're really getting in a bunch of free training. Actually you don't have time not to.