I'll try to sum it up my way.
Believe it or not, you can make a top SEO optimized site and .. fail!
Yet, you can make any SEO mistake, including over/under optimization, and Ö succeed. Because it all about quality and the readers reaction:
If they love your site, Google will notice that and reward it.
If they donít, youíre screwed no matter what you do.
Therefore, watch closely the user engagement and work hard to increase the percentage of returning/direct/referral visitors, by making your site well-written and well presented.