Google's ad serving tool, Google Ad Manager (google.com/admanager/), which launched as a beta in March is now open to all publishers. If you are a publisher using OpenAds, OpenX, phpAdsNew or a similar product, you may want to strongly consider switching to this free hosted platform.
I personally use it on this site and I have incredibly happy with Google Ad Manager for a long time. Why? (1) I don't have to worry about my server hosting the ads, (2) I don't have to patch it for hackers, (3) I don't have to pay for extra server capacity and bandwidth and (4) it is easy to use.
If you are interested in giving it a shot, I strongly suggest you use my tutorial named How To Set Up Google Ad Manager On Your Site or Blog to get started. Google Ad Manager has a ton of features, but my tutorial should get you started and then, you can explore the other features.
Why is Google providing a free hosted ad serving tool?
(1) To get more publishers using AdSense, because they make it incredibly easy to rotate AdSense ads with direct ads. (2) To get metrics and data from larger publishers.