"We're taking the approach that you put that in the requirements part of your documentation for the skin, that in order to use functionality within the ajaxtoolkit you must set your skins to be Transitional. So it's up to the user to verify that."

I am not sure that is the best approach, and should probably be fixed before the next release.

In your experience with this, have you found it to "break" functionality in other components?  For example, I have a menu component from ComponentArt that won't render the "mouse over" effect on menu items with the XML file in place... however, the moment I remove it, they work again.  This could be an issue with how I'm building the menus because I have a test app that uses XHTML Transitional and they seem to work fine in there... I'll have to look back through the code and see if there is anything silly that jumps out at me.