Groupon, as everyone knows by now, is growing like crazy. How crazy? CEO Andrew Mason just revealed at the D9 technology conference that he now employs 8,000 people, which is up from 1,500 a year ago. That means it is growing headcount at a 433 percent annual rate. About half of it's employees are sales people. Signing up local businesses to offer group discounts requires a lot of hand-holding and sales calls across many local markets. Groupon is now in 46 countries.