Sanctioning the xhtml extension for use with application/xhtml+xm l

I've been experimenting more lately with XHTML, and not the
backwards-compatible stuff that can pass for text/html.

I'd like to hear what folks here think about the use of the .xhtml file
extension, with a fixed media type mapping to application/xthml+xml. Good?
Bad? Does it break anything?

The common way to do this is through a line in .htaccess

AddType application/xhtml+xml;charset=utf-8;qs=0.999 .xhtml

Comments?

Thanks,

.micah