The Power of Custom Workflow Activities
The first of a two part article I wrote on developing custom workflow activities just appeared on the MSDN Visual Basic Developer Center. You can find the article named "The Power of Custom Workflow Activities"
here. A second article with more details is scheduled to appear here as well.
For everyone new to Workflow Foundation I would suggest reading some intro level material first. For example my "Workflow Foundation 101" article or "Hello, Workflow" by K. Scott Allen.