In an interview I was asked a question that I\'d never thought about, which was \"We already have HTML which fulfills all the requirements of writing a web page, so what\'s
XHTML forces you to write cleaner code which is easier to maintain, renders more consistently, and easier to hook into the DOM. Comparing XHTML to HTML is like comparing a programming language that is strongly-typed to a programming language that is loosely-typed.
As mentioned above, XHTML allows you to play with SVG and MathML. I'd like to add RDFa to that list. RDFa allows you to add semantics to your content that is not covered by microformats. I've personally been doing a lot with Dublin Core and Friend-of-a-Friend.