Just about every damn weblog on the Intertron these days has a stupid button, link, icon, or other doodad proclaiming that the site is XHTML or CSS compliant. Many weblog applications actually include these doodads in their default themes, and a surprising number of those default themes don’t even validate. Next time you notice one of these buttons, click on it and see if the site actually validates. Chances are it doesn’t.
Someday I’d like to put together a database of websites that claim to be compliant but actually aren’t. That’d be fun.