If you want an easy way to check GMail in Ubuntu, or other *nix systems, take a look at CheckGmail. It's an alternative Gmail Notifier that is fast, secure and uses minimal bandwidth via the use of Atom feeds.

It runs as a system tray application that checks Gmail accounts for new mail, and it does work with multiple GMail accounts. When new mail is found the icon in the tray changes and a tooltip displays the number of new messages as well as message details. Messages can be opened directly in a browser window, and most common Gmail operations can be executed on messages directly within CheckGmail.

If you are using Ubuntu, you can install CheckGmail by typing the following on the command line:

apt-get install checkgmail