I work for a small-ish tech "startup" in San Francisco SOMA/Southbeach district that is VERY friendly to bike commuting. We have a large bike rack in the middle of our office and a shower for those with longer commute. If you look around this area of San Francisco, a large % of the tech companies encourage bike commuting with secure bike storage indoors. Many of these cater to people commuting within San Francisco so don't offer a shower, but some like mine do offer a shower. I would say 10-15% of the people here bike commute on a given day. Nice summer days could be as high as 25%.

I honestly think many companies in this part of SF would have trouble recruiting someone if they didn't allow bringing the bike inside or offer secure storage. Bike commuting is becoming very popular.

A note about the big silicon valley guys like Facebook and Google - the big use for bikes there are company owned bikes for getting around their massive campuses. Unfortunately these massive campuses are not near where a majority of the employees live so a much smaller % of employees actually bike to work, though if they do they have bike storage and showers, etc.