http://msftplayground.com/Lists/Posts/Post.aspx?List=5878e505-f9a8-4295-9d5b-056fe05f8e56&ID=105&Web=b057dbe4-f419-42c3-9205-7443e3274182
http://msdn.microsoft.com/en-us/library/ff798499.aspx
http://www.wictorwilen.se/Post/Sandboxed-workflow-activities-in-SharePoint-2010.aspx