According to W3C's validator, Google's home page has 36 errors and 2 warnings. Either Google's folks aren't following their own guidelines, or they haven't implemented them yet.
I'm also concerned about not using closing tags for paragraphs, which as far as I know is still a recommended practice. Also, I've always been under the impression in CSS, there are to be no spaces in declarations:
color:#fff; (correct) vs. color: #fff;
I'm sure I specifically read that at W3C, but Google used a space in its guidelines. I hope we aren't heading to a time where we have to create multiple style sheets for different browsers or search engines to make them happy. I can still remember a time when I created different html pages for Netscape and IE to get them to display the same, and it was time consuming.