So said Jonathan Zdziarski in his O'Reilly webcast today, in which he also demoed a way around the iPhone passcode lock, as promised. To achieve that zoomy minimising effect everytime you press the home button (ie, every time you finish reading your text messages, emails, web history, contacts—think how many times you press that button), the system takes a full-screen grab and caches it. Which, if you're up to some naughtiness (or your phone gets stolen), isn't something you necessarily want to happen.
To the untrained, the cached images disappear after a few seconds, but Zdziarski demonstrated that if you know what you're doing (and you've got over an hour), you can recover the file system and see many, many of these grabs. Gadget Lab is also reporting that Zdziarski said forensics experts have actually used this method to solve serious crimes. You can probably count on two hands the number of people like Zdziarski who actually know how to accomplish this, so it's not like small-time thieves are getting their iPhones scanned regularly. But still, interesting development in iPhone security. [O'Reilly, Gadget Lab]