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Forum Moderators: phranque
Crawlers for the big search engines don't care if the pages are not validating.
That would depend on what the validation errors were. Many, maybe most, validation errors can be safely ignored, but some can prevent a page from being properly spidered. (Improperly closed tags, for example.)
Invest some effort to improve your validation, paying special attention to your main templates. It can't possibly hurt.