Until now we are a pure Microsoft Shop for delivering solutions for the enterprise and went with WatiN. This may change in the future.
As a more recent source:
Microsoft printed in MSDN Magazine 12/2010 a BDD-Primer with the combination of SpecFlow with WatiN (cool BDD-Behavior Driven Development). Its author Brandon Satrom (msft Developer Evangelist) has also posted in December 2010 a Video Webcast teaching in detail 1:1 his above findings.
There is a Whitepaper from 04/2011 on Supporting ATDD/BDD with SpecLog, SpecFlow and Team Foundation Server (Acceptance Test Driven Development/Behavior Driven Development) from Christian Hassa, whose team built SpecFlow.
