Elliotswan discusses the pro’s and con’s of standars versus validation. Basically his point is that a page which doesn’t validate but is cross-browser-compatible instead (thru using non-validating elements) is more standards-compliant as a validating page which doesn’t work in most browsers.
I often find that cross-browser compatibility requires using non-validating elements, for example: I’m a fond user of a <noscript><style>…</style></noscript> snippet which doesn’t validate but allows non-javascript browsers to access certain otherwise non-accesible site-elements instead.
Read the whole discussion here.