I take the bus everyday to work. My primary motivation is not to save money. It's simply that the bus is faster than if I were to drive everyday. Plus I hate just sitting in traffic. On the bus I can read at my leisure, respond to e-mails and even take a nap.
Just out of interest, I tried the transportation calculator to determine how much money I'm saving by taking the bus. And it's a lot. $1288 per year. So it's definitely a win-win for me.
However, the interesting part I found was that if I didn't have to pay for parking, I would actually lose money by taking the bus. It would cost me $823 more to ride the bus to and from work than if I were to drive.
So the morale of the story is, check out the commute calculators, here is a link to the Seattle Metro calculator.
Remember though, that riding the bus has benefits to the environment and is a much more relaxing experience. Also remember if people who ride public transit, hopefully we'll have a more extensive system and ultimately more cost effective pricing.