Last Thursday I rode into work on my bike with some friends. I usually take the train most of the way then bike the last two miles, but we did the whole fifteen-ish miles. (Actually, my friends are nuts, and started in San Francisco - another twenty miles away.) It's a lot easier to maintain a fast pace in a group than alone, so we averaged about 16 mph over the one hour ride. My friend also knew of a much better route through Palo Alto which definitely shaved off some distance (hint: turn off Middlefield and take the Embarcadero bike overpass over the 101 and continue on the other side of the freeway, where there is no traffic). This was pretty cool because I remember a time not too long ago that I couldn't do 16 mph on a bike at all, much less for a whole hour.
One advantage of riding on the bay side of the 101 is that you get to watch the freeway traffic creep forward. Yesterday, as I was stuck in that freeway traffic in the rain, I saw some hardy bicyclists cruise past on the path in the distance, undoubtedly making better time than me. But at least I was dry and toasty warm.