The thread started by Elliotte Rusty Harold (super smart guy, and a colleague of mine) called Why XHTML is provoking a number of intelligent and articulate responses. Here's my take:
"I'm pretty certain that the web itself wouldn't have succeeded if xhtml was required from the beginning, because a web that renders and displays documents is a much better web than one that throws validation errors all over the place."
"Five months ago, I underwent a crisis of faith after reading a draft XHTML 2 specification that was deliberately incompatible with XHTML 1 and HTML 4. For weeks I was unable to work on my book, Forward Compatibility. The title seemed a lie."
"[...] But what I feel like is being implied in the effort to get more people to embrace standards compliancy is that coding a page in valid XHTML with valid CSS involves improving the semantic meaning of the content...which is just not true."