Here's a photo I took while riding this AM.
First off - I don't ride around pretending I'm Annie Leibowitz, we were on a smooth shoulder, no traffic behind us, no real threats, and I didn't spend much time setting up the shot. Don't take this photo as an endorsement of stupid things like texting while driving. If you decide to do photography on your bike, don't do it absentmindedly.
The three riders I was behind represented a spectrum that shows bike commuting isn't limited to any specific segment these days.
1) The guy in front was dressed nicely for work, riding a road bike, and had just gotten off the Caltrain I was on, having boarded in San Francisco. He was using a backpack - more typical of someone who is just "going to work". His fitness matched his bike, not his backpack. He was probably in his late 40's.
2) The Pen Velo guy I had been chasing on Central Expressway for a mile or so without much success. He had come from somewhere North of Mountain View and 7 miles later when I pulled into nVidia, he kept going. Full kit and a messenger bag. 35-45 years old.
3) The third guy was on a hardtail Mountain bike with slicks, T-shirt, shorts. He turned onto Central at Whisman and saved me because he knew the Pen Velo guy, who then slowed allowing me to latch on. Panniers. He was also pretty fit, but when Pen Velo decided to amp it up and I followed, he let us go (I think he was almost to his office). Early to mid 30's.
We were cruising along when this photo was taken, I figured Pen Velo would drop the hammer sooner or later and it would be best to just sit in and wait for the ride. I even gave him a couple of lackadasical pulls. Note that we had also just passed someone on a knobby tired hardtail. 5 riders on this same stretch of Central Expressway, only 2 of whom had come from the magnet that is Caltrain.
No women in this photo - but there were 4-5 of them on the train with me (out of 20 or so riders for the trip on our 16 capacity bike car that was full from SF).
The numbers of bike commuters compared to 11 years ago when I started commuting with bike/caltrain? There is no comparison, the increase is impossible to miss. In San Francisco it's a bike traffic jam on Valencia, Division, and Townsend. On the Peninsula, the roads are more wide open and the destinations more spread out, but I usually see someone on a bike crossing at every major intersection I pass on the way to work, either going through his green light or waiting at a red as I roll through on green.
You can do it too. Bike to Work Day is May 14.