I'm working on a LOB framework, with an SL and MVC frontend, WCF backend, and few service modules that run on the server. I've been looking at the Spec#, to see if it helps me in any way. The non-nullable types and the checked exceptions are very good by themselves, but I yet to find any specially good usage for the contracts. What are the pros, cons of using spec#?
Also, does the spec# license mean I cannot use spec# in a project which results in an application being sold to a paying customer?