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They could be upgraded to support simple mouseover actions. For example: spidering the *display* url and showing basic advertiser info.
Why? It would help the visitor check out advertisers before clicking an ad. And it might increase CTRs, which would be great news for Google and advertisers alike. A win, win, win.
Oh, and I almost forgot. Yahoo and Microsoft don't do this ;-)
I've been watching some developments in display for a while now that have a similar approach. One fellow in particular is claiming some very high conversion rates for interactive display ads.
And Google's display builder has some mouseover templates.
So I feel interactivity with ads (any type) has a lot of potential.
plus google has to keep the publishers happy. at some point the click-through rate will drop so low that publishers will start dumping the ads for something more profitable.
As an advertiser: sure it might work if you're the only one, but imagine every other ad doing the same.
E.g. the earlier mentioned preview tool / link-enhancer of amazon: it doesn't work for my visitors: they almost never click on it, and even less do they buy things through it (I run a very few just to keep touch if this ever changes, but it's so miserable I might as well remove those last ones too). Regular links, "buy" buttons etc. do work quite well on the same site.
As a user: one more reason to use an ad blocker: I move my mouse and all sorts of ads think they need to interact with me: no thanks!