I am in the process of writing two new MSDN articles. One on creation of custom site definitions and all the CAML involved with it and a second one on SharePoint application blocks. One thing you need when making your changes to all of the CAML XML files is a good XML editor. VS.NET is not a good one :-) There are a lot of excellent commercial products available, but I stumbled upon this very nifty free XML viewer/editor from MindFusion. Excellent stuff.

Update: David is right, this Altova free downloadable home version of XmlSpy is much better. Thanks David.