Fellow VB.NET Developers,
I have posted a comprehensive article that includes two videos on Authoring Debugger Visualizers. The article also covers how to debug visualizers.
You can read the post on my blog here: http://karlshifflett.wordpress.com/2008/01/20/sample-series-authoring-debugger-visualizers/
or the Code Project article here: http://www.codeproject.com/KB/vb/AuthoringVisualizers.aspx
Enjoy developing your own visualizers!