To add to this (and as patio11 has said several times in his articles) OKCupid does this with regularity, and has provided a people with great deal of entertainment and information value, and have been covered many times in the press. They've also possibly indirectly helped their business doing this.

http://blog.okcupid.com/

KISSMetrics is another:

http://blog.kissmetrics.com/