This is my first post so I'm trying to make a grand entrance.
I'm glad to see all the advice, and wish that I had gotten some of it before I tried to commute the first time: Some back ground:
I like to ride my bike, however, driving was so utterly conveint. As running was killing my knees a little and I wanted to do more than swim, biking to work seemed ok. I drove my bike route twice.. and had done a lot of weekend riding. My first trip out, a man jumped out of the bushes on a longish up hill stretch.. Luckily, I turned away fast enough and was able to aim back down hill so that I could pick up speed to get away. The next few miles were a little hard. Stuff that didn't occur to me - road conditions (rocks from construction, cracks in the street) were a hazard at least, and down right frightening. It never occured to me that I didn't have a light to see in the dark with. I didn't give up, but after several flats and some more money for a light etc.. And not taking into account the tired factor etc.. I gave up..
Since I've got a monsterous Jeep with a thirst for gas (14 mpg) on a longish comute (35 miles round trip), I started to research it. I found a free ferry that elminates about 10 miles for me (I don't have to ride up silver strand higway).. picked a better (although steeper route) discovered the wonders of pepper spray, and also figured out ways to identify the "clean" problem. One thing I"ve done is kept a wash cloth here at work and then simply done a fash wash when I get to work. One day a week I haul extra socks, underwear, etc, and work has graciously given me a locker that I can store my uniforms in so I can come in bike clothes, making the commute that much easier.
I'm on my second week now, and aside from some soarness, I'm doing much better ego and energy wise. Now, if I could just solve my problem getting flats all the time.. Being prepared ahead of time.. makes a big difference. I road more building up to this so that the shock of riding 30 miles round trip would not make me loose sight.
My cost savings (not including maintenance and tires) by rideing is just at 5 dollars a day. If I ride 4 days a week (wednesday being supply day and rest day), it adds to 20 a week, and 80 a month.. Probalby more, as I don't have the temptation to run a silly errand around work.. I used to spend about 30 a week on gas, it would be more with new gas prices.