Forum Moderators: open
GoogleGuy himself posted that "... we don't penalize for HTML errors ...", see msg #10 in [webmasterworld.com...]
What this really means is that, if your browser can show what you intended, Google will find the content. Of course, if you put a comment tag high up and forget to close it you may lose the rest of your page, but that will show up on your browser.
That said, I believe in validation. Not for the sake of Google, but for a host of other reasons. But such a discussion belongs on the HTML forum, not here :)