XML Documentation supports native C++ without templates. So in fact it does not support modern C++ code.
The problem is even larger as not only documentation on templates is not supported but having it leads to undefined behavior so even people satisfied with structured documentation in the code and no need for its advanced uses cannot use it with templates. (Another issue would be lack of template-specific tags.)
I hoped this will change in Visual Studio 2010 but as it appears it did not. Is this going to be changed? If so then when?
If not then just removing the "undefined behavior" and adding tags for templates support (so that documentation can be written now but used later when support will be ready or by external tools) would be an improvement too.
See also forum thread: http://social.msdn.microsoft.com/Forums/en-US/vcgeneral/thread/41ea47ec-10eb-406d-b5c2-6bde62fb66c8/.