tedster - 8:03 pm on Apr 15, 2011 (gmt 0) [edited by: tedster at 9:55 pm (utc) on Apr 15, 2011]
I'd say there's a good reason to look at ads specifically, as well as other page elements that obscure the content. In the original interview with Matt Cutts and Amit Singhal [webmasterworld.com] they specifically called out excessive ads as one of the factors in the initial training criteria.
There was an engineer who came up with a rigorous set of questions, everything from. "Do you consider this site to be authoritative? Would it be okay if this was in a magazine? Does this site have excessive ads?"
[edited by: tedster at 9:55 pm (utc) on Apr 15, 2011]