Open-bars, all-night-parties, superbowl commercials (Don't believe that one?! How about cat herding?), bagel guys, sock puppets, Craig's list, and a little company called Google - the dotcom euphoria of the late-1990s hit San Francisco as hard as anywhere, both on the way up and the way down.
With the recent explosion of Facebook, Twitter, Zynga and most-recently Instagram (the latter three in San Francisco) - questions of a new boom/bubble return... only hindsight will tell, but it's always safer to enjoy the free drinks along the way :)
The bay area has a relatively long history of technological innovation going back to at least the founding of Hewlett Packard in 1939, including Intel, Xerox PARC, Apple, Google, and many others - but primarily in the Silicon Valley (aka, in and around Palo Alto) - whereas the late 1990's boom and especially the current one have a lot more action in San Francisco.
For toe-dipping (or more!) in the startup launch party circuit, plancast often has some options... while squidlist, Public Works, Maker Faire and Burning Man orient more towards the techno-artist-hippy segment of bay area tech culture.
