Does W3C Validation Matter?
I always get a good laugh when I see discussions on the whole validation and SEO argument. I have seen people damn near kill each other over this issue.
Hobo-web.co.uk (sweetest logo ever) of Scotland has conducted a test that while far from conclusive, is certainly interesting and opens up a question in my opinion that has many a webmaster scratching their heads. How does Google decide which version of duplicate content to use? In their experiment they have four pages that are the same content, same anchor text from the same page. Only one of the four versions of this page validated correctly at W3.
Guess which page Google chose to index. Yep, the one that validated.
Hmmm. I would love to see a large scale version of this. Compliments to whole “Mythbuster” idea looking forward to more.

May 14th, 2007 at 10:41 pm
See http://groups.google.com/group/Google_Webmaster_Help-Indexing/msg/5ef369e2ce4f6b8c for a statement by a Google employee
I did something similar on a slightly larger scale - not conclusive, very volatile, things go in and out daily, it all depends on when you check the numbers. My conclusion was: small things don’t matter, big things waste potential value (eg missing/unreadable “title”).