The book and the URL that you mention were already included in the Files
section of the Yahoo forum. In fact, I have included pointers to most
resources (books, articles, docs, samples, etc.) that I have found in the
last 2-3 years. But it is worth to mention the book explictly because it is
a must have.

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Carlos J. Quintero (Visual Developer - .NET MVP)
FAQs, Knowledge Base, Files, Docs, Articles, Utilities, etc. for .NET
addins:
http://groups.yahoo.com/group/vsnetaddin/ (free join)
> In addition to the newsgroup Carlos pointed out, I can recommend a couple
> additional resources:
>
> "Inside Visual Studio .Net 2003" from MSPress.
> http://www.msdn.microsoft.com/vstudio/extend/
http://www.microsoft.com/downloads/details.aspx?familyid=3ff9c915-30e5-430e-
> 95b3-621dccd25150&displaylang=en
>
> That last link is to a good number of addin samples that are written in
> C++, C# and VB .Net.