For most people/sites, there is no advantage to using XHTML over HTML, if you measure "advantage" in business terms (does it increase the bottom line?).

I worked for a company where I started implementing XHTML because it did increase the bottom line, though, at least in terms of efficiency for single sourcing solutions. Because XHTML is XML, that uses HTML tag names for it's elements, you can parse XHTML just like XML but it also works in Web browsers.

We used it to create HTML Help files that could also be converted into PDFs.

So if you need/want to convert your HTML files into another XML format for other applications, then XHTML is the way to go.

Maybe in the future (5 years) XHTML will be more necessary on the Web as XML becomes more supported and expected in end-user applications. RSS is XML, for example.

Did that help?