Google made some rather significant changes to their AdSense policy recently and most publishers are, well, pretty happy about the development.
The company is essentially taking an entirely different approach with its AdSense publishers and is now providing some very detailed guidance about the proper placement of ads.
In the past, AdSense publishers were able to place a maximum of three AdSense content units, up to three link units and up to two search boxes on each page. As you might imagine, publishers tend to get hung up on the numbers aspect and often ignore what is really being said by Google - that they care about the user experience and the quality of impressions being sent to their advertisers (and don't want consumers overloaded or misled).
Under the new "Valuable inventory" section in the AdSense policies (https://adsense.googleblog.com/), Google provided examples of pages/websites with AdSense that will be considered unacceptable in the future including those "mirroring, framing, scraping or rewriting" content from other sources without adding value, those sites with pages offering more advertising than publisher-provided content, as well as automatically generated content without manual review or curation, and hosted ad pages or pages without content.
Google also went into some detail about other instances when ads are simply not going to be appropriate. AdSense now recommends that ads do not appear on thank you, exit, log in, or error pages, that they do not appear in dynamic content, in email, within a software application, in a new window or pop-up window, or behind a login.
On the whole, these are good changes that should encourage publishers to rethink the way in which they are integrating advertising on their site. It should also serve as a warning, even though they are no formal restrictions, to keep ads to a minimum (as more ads often means a lower CPC on average).