Google Maps Mania reports that for a short period earlier this month, Google began featuring in-map advertising, in the form of smaller, sponsored markers. This has since been removed, but it is yet another sign of the coming shift toward mapping as a major area of browsing. As Google continues to develop Google Local and Google Earth, the services will increasingly become a form of browsing in their own right.
A lot of people have perceptively drawn parallels between Google Earth and Mosaic, the precursor to Netscape.
Link to Google Maps Mania
Also, a great resource for Google Mappers is Mapki.com, which has developer tools for Google Map hacking, as well as a huge index of examples of Google Maps hacks.