I just blew up a site by attempting to create a web part page in one of the custom MSFT WSS site templates just recently released. Tread carefully.
Like anything new and cool, there are bound to be bugs. I heavily suggest that all experimentation with these templates be just that… experimentation. Try this stuff out on a development box or a Virtual PC image first.
UPDATE 8/12/05: More posts on WSS Application Template issues: