Although Google Gadgets Sidebar is still in an early phase, it's pretty stable and looks very similar to Google's implementation. A limitation of this extension is that some of Google's official gadgets (Gmail, Google Bookmarks) don't work because their code is not available in the source of the gadgets. Others (like Google Calendar, Google Reader) are available.
The advantage of this solution is that you have the gadgets in front of your eyes as long as you keep Firefox open. You don't have to use Google Desktop or Google's Personalized Homepage and, for most gadgets, you don't even have to be logged in.
The main disadvantages are that you have to find the address for each gadget in Google's Directory and that the extension and Google's homepage aren't synchronized.
How to add gadgets to the extension?
* go to Google's Directory
* search for the name of the gadget
* copy the address of the xml file
* paste the address in the "New gadget" input box (in the sidebar)
The extension can be installed only in Firefox 1.5. If you have Firefox 2.0 or above, download the extension, rename it to zip, open the the archive, replace <em:maxversion>1.5+</em:maxversion> with <em:maxversion>3.0</em:maxversion> in install.rdf and rename the file back to xpi. Then drag the xpi file to your browser window.