I would like a better story around BDD style development.
Take a look Cucumber (cukes.info) for Ruby on Rails. The tool is fun to use and helps me think in terms of the behavior of the application that I'm trying to build.
BDD, ATDD should allow business users to create new tests without intalling/using Visual Studio and via a web interface. See Fitnesse http://en.wikipedia.org/wiki/FitNesse.
SpecFlow are great if only developers specifiy the tests. This helps but does not let the business users, QA, etc creat their own test with their own data.
Pekka Ollikainen commented
At the .NET and Visual Studio , SpecFlow is easier to take under hood
NBehave also have Visual Studio support, http://visualstudiogallery.msdn.microsoft.com/9ea87b8a-4086-4a02-984c-be4b3663b6cb
Take a look at SpecFlow. Gherkin is implemented in Visual Studio in detail.