Since K2 [blackpearl] is built on top of Windows Workflow Foundation (WWF), I felt it would be important to bone up on WWF before the release of BP.
I've been going through hands-on labs provided by Microsoft on WWF. So far, I have found it to be a decent primer - hopefully you will to - if you've had little or no exposure to WWF. Though, while learning WFF, I'm amazed how low-level (and complicated) it is compared to K2. SourceCode has definately done a good job creating a powerful platform that abstracts the complexities of building workflows, while still allowing for great customization and complexity, when needed - the best of both worlds, really.
You can download the Hands-on Labs for Windows® Workflow Foundation in C# and VB.NET from Microsoft here.
Overview excerpt from the downloads page:
"This download is a set of 10 Hands-on Labs for Windows Workflow Foundation in C# and VB.NET versions. These labs are suitable for a .NET developer with 6 months experience who wants to learn about Windows Workflow Foundation. Each lab is approximately 60 minutes of work. The download package includes lab manuals for each lab, pre-requisite files for the labs and sample completed solutions for each exercise in the labs."