In the full PDF they released today, I thought the screenshot of the "mortgages" search was particularly awful looking, far too many ads and clutter -- even the Google box read like an ad. The rest were interesting. I didn't read enough to find out how to get placed as a third-party alternative. I imagine it uses microformats or some other similar metadata, which will quickly become popular. If there's payment for the third-party links, might I suggest Google that you show fewer AdWords ads? A white sidebar would go a long way to cleaning up these enhanced pages by giving the eyes some space to rest on.