Very nice wp plugin. Excellent for SEO 'newbie' just like me. I am still expanding my blog Fragaria from the SEO point of view, so I can't write how my rank of my site is growing.
My little clue:
To keep blog valid for validator.w3.org just edit class all-in-one-seo-pack/aioseop_class.php and put missing
//<![CDATA[ after every
//]]> before ending tag