I wouldn't know any statistics but, in general, Silicon Valley is much more centered in the South Bay and than it is in San Francisco and those who work at Adobe, Sun, Apple, Oracle, etc. would normally live either on the Peninsula or in the San Jose area.
Just to take Apple as an example, in general, it is pretty crazy for the thousands of people who work in Cupertino (which is immediately adjacent to San Jose and is some 50 miles from most points in San Francisco) to live somewhere other than the South Bay or at least the Peninsula - from which locations the commutes would be pretty modest (still likely 20 minutes or more for most people but not the hour-plus it would be from the City).
Some people undoubtedly live in San Francisco while working at Apple simply because they like the City so much and prefer to live there in spite of the long commute. But these would likely be unusual exceptions and not the rule.