NOTE from DearMYRTLE: The following was posted by our friends at the Lifehacker blog.
Gmail Glitch Seemingly Wipes Everything from 150,000 Accounts (So Back Yours Up Already) [Backup] - Lifehacker
by Kevin Purdy on Feb 28, 2011 5:02 AM
About 150,000 Gmail users, or 0.08 percent of the webmail service, logged in over the weekend to see everything gone—email, chat logs, contacts, and attachments. Google's working to restore the accounts, but in the meantime, take it as another vivid reminder of the value of local backups.
For more information about Gmail backing up strategies, see the original blog post.