Very good info Bobby
I'd like to add one other factor, very often overlooked, is having valid html/css code. While i don't have a solid case study, it's been my experience that valid documents rank better.
Not to mention, it's just a good practice anyways, as having valid code will prevent most cross-browser "surprises" and make your site more accessible. Validation check tools can also alert you to where you may have forgotten alt tags on images, etc...
I recommend using this free validation tool: http://validator.w3.org/