The first session today here in Zurich (cold!) is going to be about the Windows Workflow Foundation limiting myself to WF and the use of it in WSS/MOSS 2007. There is of course always a lot of interest in workflow and although it looks easy when you start exploring the OOB workflows and the design of new ones with the SharePoint Designer, you should not underestimate the effort it takes to create real-world custom workflows with Visual Studio.NET. So any resource to learn from is helpful, no?
One of the best resources in the blogging community is Carlos Segura Sanz who frequently has excellent postings on the topic. His latest one for example is an introduction to WF and the ways you can host WF in you own Windows application. It is in Spanish but hey.. no problem for me :). Take a look at the small sample app he has available as download illustrating the techniques.
Two other ones that are extremely useful if you are interested in how you can extend the SharePoint Designer with custom activies are: