Google's new “Page Layout” algorithm gives penalties to websites with too many ads above the fold.
Certainly this is a frustration for many users that do a search query only to keep landing on sites crammed ads and no consideration for user-experience.
Google acknowledged their users' frustrations in a recent Search blog post:
We’ve heard complaints from users that if they click on a result and it’s difficult to find the actual content, they aren’t happy with the experience. Rather than scrolling down the page past a slew of ads, users want to see content right away.
Their warnings have also been posted on the Google Webmaster Central blog, as well.
For webmasters that are concerned about their site's search ranking. One tool that can help would be the Google Browser Size tool, which gives an understanding of relative browser size to a website's content. The Google anti-spam team is not planning on providing any tools for measuring the safe number of ads to page content. Perhaps it's the best thing. Rather than giving the formula for the maximum allowed ads vs page content relative to a page, it Google makes it a little more vague than web designers need to focus on best-practices, which is ultimately better for the user and less about gaming the system.