It looks like the research project Spec# that Microsoft has been working is available to download and play with. Obviously I am behind on the times as this stuff looks like it has been available for some time.
From what I understand from feedback form the ALT.NET event in Seattle and the channel 9 videos (http://channel9.msdn.com/shows/Going+Deep/Expert-to-Expert-Contract-Oriented-Programming-and-Spec/ & http://channel9.msdn.com/forums/Coffeehouse/226756-Using-Spec-in-VS-2005/), Spec# aims to provide us with compile time verification of what constitutes a method or class contract. Just as the shift from VB to .NET meant I had access to a strongly typed world, the shift Spec# looks to offer is further verification on a class or method contract. At a basic level this gives verification on null parameters and some contractual awareness of exceptions.
I doubt there is any production value in what spec# provides at the moment, but is worth keeping an eye on as the expectation of reliable and durable software keeps increasing.