I would like to add a comment to point 14 (Valid code):

Until recently Google, was recommending webmasters to adhere to their guidelines. But now Matt Cutts at Google said, that we SHOULD adhere to the webmaster guidelines if we want our sites to stay in their index. More: SMX - Googles Matt Cutts on their webmaster guidelines.

So what about this Guideline? "Check for broken links and correct HTML."

Am I missing something again?

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