How to shoot yourself in the foot
There are folks who recommend the use of XHTML over HTML, in the interest of promoting web standards. While this idea has some merit, I have chosen to use HTML 4.01 (strict) as the basis for my work for the simple reason that IE6 does not actually know anything about XHTML. IE6 will be with us for many years, and the degree to which IE6 "supports" XHTML is more-or-less accidental.
It just occurred to me that - to an extent - promoting the use of XHTML now may actually be harmful!
Let us say that Microsoft re-starts IE development, and decides to support XHTML. They face an immediate problem. There are an unknown number of web applications of in the field that have adapted to the partial XHTML support in IE6. If the Microsoft IE team implements exact standard XHTML support, they run the risk of breaking existing applications! This is not a good thing, so they may (reasonably) choose NOT to change the existing IE behavior for pages that declare XHTML 1.0 or 1.1 as their DOCTYPE.
The only way that Microsoft can fold XHTML support into IE without the risk of harming their customers, is by keying their exact-standards-compliance to a later version of XHTML. Anyone up for XHTML 1.2? (But not too soon, or we run the risk of "spoiling" that revision as well).
So the folks evangelizing the use of XHTML now have put Microsoft in a position where they cannot implement exact XHTML compliance without the risk of harming customers.