There's another new sample up, written by one of our testers Charlie. This sample shows how the WF Rules Engine can be used to process rules on Xml documents. This is something BizTalk BRE customers were able to do inside the Business Rules Composer, but is not obvious how to do with the WF Rules engine because of lack of first class tooling. However, since all the WF Rules Engine deals with is a .NET type, if you can convert your data as expose it to the engine as a type, you can easily accomplish the scenario.
Get the sample here - http://wf.netfx3.com/files/folders/rules_samples/entry8981.aspx