Your markup validator, whether it’s the one on the W3C site or one built into your favorite coding tool, is not a measuring stick for greatness. It’s not to be used on other people’s code for the purpose of pointing out their shortcomings as a markup coder so that you can make yourself feel better than them. The fact that your code passes a validator does not make it better than the next guy’s code.

Jeff Croft: Your markup validator