How to use Thunderbird with GUMail: New Features in Thunderbird 2.0:
Quota Meter

If you have reached 75% of your quota, a handy meter will appear next to your message count total in the lower right hand corner of the screen with other e-mail statistsics.

As soon as you see this, you must begin to clean your e-mail folders and delete mail. Remember you can save important e-mail in local folders as well.

Click here to find out more about using local e-mail.

Other new and improved features can be read about at http://www.mozilla.com/en-US/thunderbird/2.0.0.0/releasenotes/.