Allegedly, Tiwtter's plans for taking over the universe, 1 billion users and finally finishing off Google, which were boldly hosted on Google Apps, were stolen by recycling someone's old deleted Hotmail account and requesting that person's Gmail password to it.
Why is it a problem and why is it bigger than one-time screw-up by some Twitter employee? Because (1) Google account model makes it very easy to mix personal and business, and the two have drastically different security requirements, and (2) a company's intranet has an infinite number of defenses such as locked-down, encrypted laptops with biometrics, etc., and security of the stuff on the intranet is carefully watched by professionals. With Google Docs or any similar cloud service for that matter, anyone is their own and their company's sysadmin: it's enough to get just one person with a weak password on this weird business-personal hybrid called "Google account" and the whole company is exposed.
This is a big setback for Google Apps and the entire cloud model of operation: once the data leaves your company, it's much harder to lock down and this needs to be addressed in order for this whole cloud thing to work.