I just calculated how much my commute costs me at today's gas prices, just the fuel cost, not the wear and tear on my car. It is about $5.70 if I drive in and about half that if I carpool (I drive to a park and ride and meet my carpooler).
If I took public transportation, it would cost $3.40 each way (less if I bought monthly passes), involve three buses, and take up to two hours. Not really how I want to spend my time or money.
I did have one job where I took the bus. It was convenient, though I did have to make arrangements with my manager to work a half hour more every other day so that I could leave a half hour early every other day to catch the bus. At that time, gas was cheap, but I didn't own a car so I didn't have much choice. I didn't mind taking the bus since the stop was only a couple blocks from my house and it stopped right in front of my workplace. Granted, it took twice as long as driving, but I didn't mind since there were no transfers involved. Like I said, convenient.
Right now, I'm looking into carpooling with more people. My current carpooler's schedule only allows us to carpool one or two days a week. My occassional carpooler just gave notice. With gas prices being what they are (and the whole going green thing), I'd like to be carpooling four or five days a week.