Fundraising? I thought they were making money hand over fist. What is up with all these Silicon Valley "success" stories that can't get profitable enough to s

Fundraising? I thought they were making money hand over fist. What is up with all these Silicon Valley "success" stories that can't get profitable enough to sustain themselves w/o more financing (e.g. Facebook, Twitter, Mint, etc). Fundraising is fine early on, but these companies are pretty big and mature. When do you actually start turning a profit? We have some weird definitions of success in the valley.