I've only been here six years, and truth be told I avoid SF at all costs, but all I have to do is look at the job listings. SF listings are full of every Social Web Media Infinity-point-Fad known to man.

South Bay -- Platforms, infrastructure, embedded systems, established technologies, emphasis on availability and reliability. This is what the San Francisco startups rely on to make sure their new web startup doesn't fall over at the first sign of traffic.

One might see this as the traditional Silicon Valley maturing and even stagnating in comparison to San Francisco's young, hip, fast-moving culture, but I don't think it's reasonable to treat them as a unified entity.