Well, there’s a lot to it. The Bay Area is really divided into four sections: East, North, South, and Peninsula. All areas have their nicer and their less nice areas. Oakland and the cities along the east shore of the bay are not so great and I wouldn’t recommend them. Definitely more racially diverse, but more crime and more crummy neighborhoods. Further into the valley on the east (Walnut Creek, Danville, San Ramon) are nice and hilly and very suburban sprawly and white bread, but they’re a bit far from SF. The north (Mill Valley, Larkspur, Sausalito) is pretty nice and expensive, but close to SF. The peninsula has its share of nice areas (Atherton, Burlingame, Hillsborough, Foster City) and its less nicer areas (South San Francisco, East Palo Alto, San Bruno). All of those are close to SF and are along Highway 101 and I-280, which go straight into SF. The South (San Jose, Sunnyvale, Santa Clara, Palo Alto) is very upscale and full of computer companies. It’s also very crowded and congested and has a warmer climate than most of the Bay Area.
Within San Francisco, the nicer areas are places like Sea Cliff, St. Francis Wood, Russian Hill, Pacific Heights, etc. They’re all not too far from downtown. I’m sure you may know about Castro, the Mission, and the Haight. Lots of places for young urban professionals. Hunter’s Point is a place to avoid.
Okay, that wasn’t very succinct. I can definitely answer more questions if you have them. I’m pretty damn familiar with the Bay Area. :)