I feel that specification frameworks can muddy the intent of a unit test with a lot of ceremony. It is nice in theory, but implodes as soon as someone asks you to modify a specification. Where as a simple XUnit fact or Nunit test is flexible and clear in intent (if written correctly). Let's face it too, most business users are not handing you specs that you can plug write into your favorite BDD framework. That's my rant, hopefully nothing too controversial. If I had to use a BDD framework, I'd go with MSpec.
I feel that specification frameworks can muddy the intent of a unit test with a lot of ceremony. It is nice in theory, but implodes as soon as someone asks you to modify a specification. Where as a simple XUnit fact or Nunit test is flexible and clear in intent (if written correctly). Let's face it too, most business users are not handing you specs that you can plug write into your favorite BDD framework. That's my rant, hopefully nothing too controversial. If I had to use a BDD framework, I'd go with MSpec.