Unfortunately for those looking to jailbreak their device (and there are good reasons to do so), this vulnerability was the driver for the browser-based jailbreak, JailbreakMe.com, that Adrianne Jeffries wrote about two weeks ago. If you upgrade to iOS 4.0.2, JailbreakMe.com will no longer work (for the moment, anyway; the second iteration of JailbreakMe.com is already underway) .
While losing the ability to jailbreak in the browser may be disappointing, losing the ability to have a malicious coder take over your iPhone with a rogue PDF is not a bad tradeoff. As iPhone usage becomes more prevalent in the enterprise, the onus on Apple increases to ensure that such security lapses are found and fixed quickly. As Sarah Perez noted earlier this week, a more secure iPhone could be a competitive advantage for Apple against Android phones that are starting to see more malware.