But is it profitable? I have built a fun, big site in the past, but I couldn't keep paying for the servers. Now I know it's not as easy as "build something cool, users will come, and money will follow"
It a perfect example of executions and networking/inside deals. Yammer has always been violating on multiple Facebook patents and one would think that once Y became a heavyweight someone at FB legal dept would have pursued the suit. But they hadn't. Only later on to be bought by MS, which has its own stake in Facebook. Rest assured, had you pull the "Yammer startup", you would have been bombed with cease & desist letters from FB until you bleed the last drop of sweat.