Since pike's post about ArrayLists I've got the bug for seeing what things VBA can take advantage of using the CreateObject() method. I've been looking around the MSDN sites at the different .NET Classes and noticed that some classes within the same namespace can be created, whilst others can't.
e.g. from what I can see (not tested all of them yet) the StackTrace object is the only thing that works from the System.Diagnostics namespace.
Is there any rhyme or reason as to why some can be implemented and others can't? Does it depend purely on what .dll files are present in the Microsoft.NET directory?