ThinkLemon also has a review up of the Google Earth for Mac beta.
Meanwhile, a friend with a current model iMac on 1.5GB of RAM is reporting utterly smooth rendering, even with a large detail area and with anisotropic filtering turned to high in the preferences.
[Update 16.39 UTC: Google has asked very nicely that I take down references to sites where you can download the application.]
Works great, but I just realized that the custom icons for placemarks does not work on the Mac version. Weird.