As far as I know, only one of those questions has been answered publicly-- the middle one, and the answer is: "a group of investors lead by Union Square Venture

As far as I know, only one of those questions has been answered publicly-- the middle one, and the answer is: "a group of investors lead by Union Square Ventures and including Ron Conway, Chris Dixon, Caterina Fake, Naval Ravikant, Nirav Tolia, Joshua Schachter, Micah Siegel, and Bob Pasker." (Cf http://blog.stackoverflow.com/2010/05/announcing-our-series-a/ http://blog.stackoverflow.com/2010/05/announcing-our-series-...) As you can see from the linked article, SO raised $6MM, but the terms and valuation have not been made public (as far as I know.)