I just posted a video tutorial on using the Workflow Studio SDK to to convert a PowerShell cmdlet to an activity library on the Multimedia section of the Workflow Studio CDN site

This tutorial walks you through creating an activity library from the Get-Date PowerShell cmdlet just like the tutorial in the Developer's guide. The SDK and Developer Guide is available here:
http://community.citrix.com/cdn/wf/sdks

Here is the video:

Getting Started with the Workflow Studio SDK

Get started converting your own favorite PowerShell cmdlets and let us know what you find.