I think you're right that it's mostly startups, but that's also the job market in SF right now. They far outnumber the established companies.
Also, from what I know of (fairly experienced) friends and acquaintances working at larger companies in the bay area, the financial trade-off is still pretty sketchy. A salary of $250k a year will support you well in a decent single-guy lifestyle, but it won't go much further than that.
Also, from what I know of (fairly experienced) friends and acquaintances working at larger companies in the bay area, the financial trade-off is still pretty sketchy. A salary of $250k a year will support you well in a decent single-guy lifestyle, but it won't go much further than that.