gstick - 8:46 pm on May 24, 2011 (gmt 0)
My interest was in reaching mobile viewers. The Wikipedia article on XHTML gives the impression that HTML 5 is now the interoperability horse that W3C is betting on. This supports g1smd's comment.
The article also reports that "Simon Pieters researched the XML-compliance of mobile browsers and concluded 'the claim that XHTML would be needed for mobile devices is simply a myth'". I will keep my eye on HTML 5.
Thanks for the comments.