Emitting XHTML instead of HTML is pretty popular among geeks these days and Pie/Echo/Atom (PEA) crowd is no exception. I don't blame them because I am drawn to XHTML as well like a moth to the fire. Unfortunately, it amounts to technical masturbation because there are no real benefits to using XHTML. Even worse, using XHTML can be down right harmful.
Beside the subtle semantic differences between XHTML and HTML, DOM differences, lack of clients, round-trip problems, parsing problems, editor problems, and proliferation of invalid XHTML problems, the usability issues looms above them all.
You see, many people still write HTML by hand and will continue to do so for at least another ten years. Same can be said about XHTML. But XHTML is XML, meaning you can't just put elements anywhere like you used to in HTML. It seems fine now because browsers think they are looking at HTML.
When and if XHTML browsers become popular, will they be as forgiving as HTML browsers with structural mistakes? Answer has to be Yes because people want browsers to be a Tool, not a Judge.
Can people learn to write valid XHTML by hand? My answer is No. People can easily remember names of often used tags and attributes. They can also remember certain common structures like <head> and <body> inside <html>. But they just can't keep the whole XHTML schema in their head nor put up with having to look up all the time or get caught up in a viscious edit and validate cycle.
So, I consider XHTML to be the centerfold geeks are masturbating to. I am a geek too and find XHTML to be sexy enough to ogle. But I don't expect it to cook my dinner nor raise my children. It's just an insert.