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And considering Google has a "Site performance" tool in Webmaster Tools; you can bet it is an important issue to them.
who says that valid html always results in a faster loading page?
Interestingly, Matt Cutts new GoogleWebMasterHelp video specifically addresses the speed issue today. So like I said, "collaterally" validation can help ranking as it is related to speed.
[edited by: tedster at 7:49 pm (utc) on Mar 15, 2011]
[edit reason] Added a link to the video [/edit]