Imagine loading Gmail and noticing that all your mail have been deleted. This is a real trouble for many Gmail users who thought that they lost all of their messages. Here's one of the many reports from Gmail's forum:
Yes, whatever the mistake is on Google's end (and it clearly is that, not a hack, unless it's some kind of inside hack) it's basically reset my account so it's like a brand-new Gmail account My friends are intact, but nothing else--the folders have reset to defaulting, my signature line is blank, the "theme" is changed back to the default and--of course--every single email from the last 7 years has misplaced completely.
The Google Apps position page mentions that "this issue affects less than 0.08% of the Google Mail userbase" and "Google engineers are operational to restore full access". The users that are affected "will be provisionally unable to sign in".
This is a really significant problem for Google and one of the biggest Gmail issues ever since Google's email check was released, back in 2004.
Update: A Google engineer says that the "accounts that are precious are currently fully disabled. We're in the process of altering this to be a Gmail only disable so you should regain access to other Google services soon. This will also mean email to these accounts stops lively and gets queued up for later delivery instead."