At the Google I/O conference today, VP Engineering Vic Gundotra stressed the supremacy of the browser among all internet-enabled platforms.
Peculiarly, Google is not offering the equivalent of a default installation of Google Earth in the browser. If you want to search the globe from square one, you still need to visit the 2D Google Maps website. Therefore, this release is mainly a developer one – not really a new product launch. Hopefully we’ll see a “3D Globe” option in Google Maps soon.
Update: As commenters point out, Microsoft has been 3D mapping within the browser for over a year, also only on Windows and with certain browsers.