Brian Loesgen has a summary and comparison of Windows Workflow Foundation (WF) and BizTalk Server on his blog that would be good to bookmark until more specific information is out.  While he attended the BPI and WF conference at the beginning of October, I'm going to be spending the next couple of days in WF labs, and hope to end this week with a better understanding of WF.  I spent some time on Friday with the K2 Workflow folks, and I am looking forward to an interesting upcoming 12-18 months of answering questions about the workflow triumvirate.  BizTalk Server, WF, and K2 Black Pearl... (and what about Captaris and Ultimus? - I think they'll show up somewhere).  Anyways, I expect it's going to be fun.