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The new Ad review center will show you ads of all targeting types (contextual, interest-based, and placement) that have appeared on your pages, and allow you to review them. With placement-targeted ads, you can still review them before they show up on your site. And now, rather than grouping ads together, you can make decisions on individual ads to control what appears on your site at a granular level.
I could be wrong, but I thought I saw somewhere that it was a gradual rollout, and it was going out first to the people who were already making heavy use of the old one.