I should mention that there was great disappointment among XHTML Web Author gurus when Microsoft decided to once more (as they had with Internet Explorer 6.x Browsers) not support the
application/xml+xhtml MIME type for XHTML in their Internet Explorer 7 release -- thus effectively killing XHTML as a viable Markup language for the present. I personally was not too disturbed by this as I don't think the current iterations of XHTML are "ready for prime time" anyway (XHTML 2.0 may correct all the problems).
If you are interested, visit
Serving XHTML Documents for a comprehensive explanation of the above.
James