There's some handy stuff in Google's iGoogle/Gadget directories, but getting them to work in Ubuntu Linux previously required a semi-wonky Screenlets setup. These days, you only need open the Software centre, search Google Gadgets, and get started.
The Gadgets work just like they would on a Google Desktop installation on Windows or Mac. You can either keep them constantly on top, or have them auto-hide, or activate with a hot key. Any of the desktop Gadgets, or any of iGoogle's offerings, are at your disposal. Handy stuff for some, and easy to install for anyone.