http://searchengineland.com/interview-google-search-quality-rater-108702
A fair amount of page layout & design grading in their job.
"To give you an example, a page where you can tell what the main content is with ads taking second page in the design would get a high rating. A page where the ads are confused with the main content, where you can't tell the difference between content and ads would get a low rating."