At least is a novelty for me. As you can see in the picture, there are links located INSIDE a 160x600 Ad (see the arrow at botton), and when I move the cursor over there, the status bar show a call to a Google Adsense Javascript function called "curl". But the interesting part is this: if you click one of those links the ads dynamically change, without reloading the page, to show ads related with that keyword (and showing new Keywords links at bottom too).
That's pretty cool, never knew it worked like that before. I'm curious as to how you found this out though.
I've found when checking new pages just added on my site. I remember a similar feature on 2006, but instead of keyword links, they were providing an input field, and the user needs to fill the input (with his desired keywords). That feature was not successful, probably because webmasters were filling and clicking high-paying keywords on their own ads.
Seems a feature on testing phase, because now the behavior is different, just like if were "Link Units": when users click a keyword link, they're brought to a page of related ads.
why dont you search the forum? google has started to display ads like that for nearly 4 weeks. it's an old news