As I covered at Search Engine Land, the question was posed to Google's Matt Cutts about Google penalizing their search results page because there are so many AdWord ads pushing down the organic search results.
Matt responded two ways, the second more interesting:
(1) Google doesn't index their own search results.
(2) If they did, the ad to organic results ratio and layout would not trigger a page layout penalty.
Got that? That is a good benchmark.
Here is a rough sketch of how AdWords ads layout within the almost defunct browser size test by Google:
I expect a lot of interesting and fun comments on this post.
Forum discussion at Google.
Update: It seems Matt didn't mean any example of a ad to organic ratio search results page. Check out this tweet:
@rustybrick What I said ("even if we didn't block our results, the algo wouldn't fire") is true, b/c most Goog searches have no or few ads.— Matt Cutts (@mattcutts) June 14, 2013
So, not the really heavy ad pages, but the standard ad pages. Got that?