Headline read to me "Small no name startup says they won't hire employees from huge company that's also never heard of them"
Seems all about the publicity.
Do they make those numbers public though? All I could find was this http://techcrunch.com/2010/04/26/yammer-doubling-revenue-eve...
Revenue in 2009 was “seven figures.” I asked Sacks to narrow that down in the video but he refused. He does say that Q1 2010 revenue exceeded all of 2009 revenue, and that revenue is now doubling every quarter. Yammer’s revenue goal by end of year is to be at a $10 million annual run rate.
That's not nothing, but it seems unfair to laud a company for bringing in a lot of real revenue if they don't disclose the actual number.