Episode 6 of This week in Venture Capital (TWiVC) mentions Stack Overflow. The occasion is the Series A round of funding of USD$6 Million.
They speculate that the valuation of Stack Overflow is in the range USD$15 Million to USD$18 Million.
MP3 file. 1 h 06 min 26 secs. 39 MB. Published 2010-05-12.