Palo Also is comparatively good for its area, but bicycling's modal share among commute options even there is quite low, hovering around 10%. Partly that's because many people who live in Palo Alto work elsewhere, and vice versa. In other cities on the peninsula it doesn't even crack 5%; nearly everyone who lives or works in Santa Clara or Sunnyvale drives, for example (biking's modal share is <2%). Mountain View is somewhere in between, at ~6%.
Those numbers aren't inconsistent with it being possible to bike in those cities, but they suggest that people in practice don't. Here's a map: http://www.flickr.com/photos/bike/8007583135/
Infrastructurally, it's quite noticeable as well. The Valley doesn't feel like a bike- or pedstrian-friendly place, but like a place criss-crossed by huge roads, giant parking lots, and not only interstates and state freeways, but county expressways, something I've rarely seen elsewhere (apparently the Peninsula opted out of BART and took the money that would've been spent there, to build abominations like the San Tomas and Lawrence expressways, instead). I remember walking from Mountain View Caltrain to the Microsoft campus on La Avenida once for a SuperHappyDevHouse, and it clearly did not seem like a route anyone ever expected a pedestrian to walk on.