Google Earth can now be used from a browser, without having to install the full application. Instead of the application, you need to install a plug-in that only works in Firefox and Internet Explorer 6/7 on Windows.
The samples look pretty promising, but I find it hard to understand why Google didn't use the API to create a better experience and bring more features from Google Earth (the search box, the list of overlays, the navigation controls) in a single interface.
Before downloading the plugin, please note that Google installs it in Firefox and Internet Explorer, along with a system service called "Google Update Service". The plug-in uses a lot of memory (around 100 MB just for loading the initial view and 300 MB for the Monster Milktruck demo) and, for each embedded object, you're running an instance of the Google Earth application.