As promised during my March, 2011 TSS talk on SPD, here are some resources to help you get started with this tool, in no particular order:

1. Asif Rehmani: http://www.sharepoint-videos.com/about/

2. Laura Rogers blog: http://www.sharepoint911.com/blogs/laura/default.aspx

3. Nothing But SharePoint: https://www.nothingbutsharepoint.com/Pages/default.aspx (specifically the content formerly known as EndUserSharePoint)

4. SPD Team Blog: http://blogs.msdn.com/b/sharepointdesigner/

5. John Ross’ blog: http://www.sharepoint911.com/blogs/john/default.aspx

6. Randy Drisgill: http://blog.drisgill.com/ (mostly branding focused)

7. Woody Windischman blog: http://www.thesanitypoint.com/