Did you have a scenario where you wished you could customize the creation of AppDomains? Or, you could control how many AppDomains any code that runs in your application context (e.g. if you are writing a plugin load framework) could create? Or, how about reusing AppDomains for various assemblies?
I have just finished an article on how any of the above scenarios can be accomplished using the System.AppDomainManager type, introduced in .NET Framework 2.0, by intercept AppDomain creation requests.
You can read the article at http://www.wintoolzone.com/articles/Customizing_AppDomain_Creation.aspx and download associated source code from http://www.wintoolzone.com/downloads/Customizing_AppDomain_Creation_src.zip