Here are some potential uses for the gadget:
* check your inbox from a fast-loading simplified interface
* find the email address of a contact: compose a message and use Gmail's auto-complete feature to obtain the address
* the fastest way to search Gmail: click on the Search option or type "/" and then enter your query
* preview your message while still viewing the list of messages, a feature that's not available in the standard interface
* add multiple instances of the gadget for different Gmail accounts (the gadgets works with Google Apps accounts too).
The gadget can be installed from this page and it's worth mentioning that it doesn't support notifications yet.