Available in Google Earth now, and just announced in a Google press release, (whatever happened to Google’s press-release-by-blog-post practice?:-): New stuff in the “Featured content” folder in the Layers sidebar. Some of it’s been there for a while, but brand new is a layer by the United Nations Environmental Program (UNEP), a layer by the US National Park service, and expanded global content by the Discovery Channel.
The UNEP content is vast, and wonderful. For the Three Gorges Dam, for example, you can click on links to detailed overlays showing how the dam is filling up. (Be patient with the downloads, though.) This is quality stuff. (ZDNet also has a writeup.)
[Update 14:48 UTC: As Google Earth Blog notes, the other vector layers get a reorganization. And there’s 3D buildings in Japan.]