Google's AdSense is expanding their reach once again, and it has the potential to greatly benefit publishers. By opening up competitive bidding to Google-certified ad networks, competition increases - meaning publishers could potentially earn more per advertisement than limited to bidding wars between AdWords publishers alone.
And that also means that other ad networks' targeting capabilities (geo and behavioral) will also be available to publishers' websites, possibly resulting in better targeted ads for your site visitors based on their online behavior or location. These third-party vendors will need to adhere to Google's policies, so privacy concerns shouldn't be an issue.
Publishers can also choose to allow and block specific ad networks already certified by Google. So, if you've had success with one of those networks more than another, you can customize. Or, if one ad network doesn't quite fit the feel of your website, they can be blocked. But be careful. This, from the Google AdSense Help section, details what may happen when blocking an ad network:
If you allow or block an ad or advertiser from a Google certified ad network, the entire ad network will be allowed or blocked.
If you use category filtering, all Google certified ad network tags that include ads from the filtered category will be blocked.
If you use the Competitive Ad Filter, all Google certified agency or ad network tags with URLs that you're filtering will be blocked.
Below is a video from the official AdSense blog detailing the news.