Paul Andrew and co. have just released BizTalk extensions for WF. This is a really cool piece of technology as people have been asking whether to use BizTalk Server or Windows Workflow Foundation when they want to implement a business process. This SDK allows you to avoid that choice by using both WF and BizTalk together :)
If you use WF, you can now build an orchestration and deploy it to BizTalk Server and the workflow can now use BizTalk features such as adapters, management infrastructure etc. If you use BizTalk, you can now try out the new workflow programming model while still continuing to use the enterprise features in BizTalk Server. Best of both worlds! Thanks Paul and co.