It's expensive. Very, very expensive. A teardown with broken windows, a dilapidated roof, and a giant hole in the second floor landing near my friend's house recently sold for $1 million. (Things like that are more shocking to people from outside California, but even compared to SoCal and even compared to much of the rest of the Bay Area, the Valley is expensive). It's crowded and full of traffic, but coming from SoCal nothing will surprise you in that department.
It is kind of all about tech in some circles, certainly. Practically everyone I know in their 20s who lives here works for some kind of tech company, even people I never would've expected to. I have to hear about how they go out drinking with their coworkers regularly and eat gourmet food at work every day. I know people who put almost their entire paycheck into paying rent.
It's very progressive. It's not "freaky" like SF and Berkeley, but it's overwhelmingly liberal. Lots of Asian and Mexican food. Lots of yoga studios.
P.S. You can also call San Francisco "SF". I hear my fellow Silicon Valley denizens say that a lot.