[noodle]

skype - got acquired. users buy service

facebook - advertising revenue

youtube - got acquired. primarily advertising revenue

digg - advertising revenue, sells stuff.

reddit - got acquired. displays some ads, but mostly for its parent company.

delicious - got acquired.

most startups have a plan that consists of one or more of the major 4 plans - sell something, ad revenue, license out your product, cross your fingers and hope to be bought out.

a good business relies on one or more of the first 3. the more of the first 3, the better.

[il]

More specifically: skype-profitable, but hemorrhaging money for ebay, ebay $1B in the hole facebook-not profitable, needs new investment youtube - not profitable, hemorrhaging money for google digg - not profitable, can't find a buyer reddit- acquired for a pittance, can't find advertisers delicious- don't know

See a pattern here? Other than the big search engines, I can't think of very many startups that are cash flow positive. Unless you're selling something or licensing, simple mathematics will tell you it's very hard to make millions from ad revenue alone.