One of the key concept of the new Microsoft® .NET Framework 3.0 platform is absolutely Windows Workflow Foundation (WF), the framework that enables you to build sequential and state-driven workflow capabilities into your existing applications.
I've always written in the past that WF will be always more an important part of every enterprise architectures and it will be always more a key concept on the future MS Dynamics architectures. The future Microsoft Dynamics CRM 4.0 (Titan) will be natively based on Windows Workflow and the workflow functionalities will be exposed via web, in order to have multiple target of your workflows.
But why not using the WF functionalities also with CRM 3.0? This could be an interesting architectural scenario for many applications.
Jeremy Hofmann has written an interesting article that permits you to open your eyes on this direction... I recommend to read it if you're interested on this topic.