I lived in Oakland (17th and Merrit), and worked at Netscape in Mountain View on Ellis. I took Bart + Caltrain + a company shuttle for 2 1/2 years. I tried taking buses as well - but it was a brutal grind, and not something anybody with a realistic choice would undertake. Bart + Caltrain is possible, particularly now that Millbrae exists, and you don't have to perform the absolutely wretched 4th and Townsend to Powell street transfer, which was the bane of my existence.

But Public Buses are just not seen as first, or even second class transportation in the Bay area, so most people, and certainly the vast, vast majority of Silicon Valley employees, would never consider using them to get to work in conjunction with Bart+Caltrain. They are, at most, used as part of two-segment trip. (I.E. Caltrain + Bus, Bart + Bus).

What I'm really trying to say, is that if the valley had a first class rapid transit system around the bay, so you could eliminate the transfer to caltrain, and just go from Bart -> Bus, it might be a reasonable alternative for a lot more people, particularly with company shuttles that run from the nearby bart station to the office on a regular basis.

Speaking of which - I've been away from the Bay for a few years - have they finally unified the payment of Caltrain/Bart/Buses, or are they still on separate payment systems?