the exploit you're talking about existed for 1 or 2 minor version numbers, and can no longer be exploited (including by the device owner) due to the OS version(s) no longer being installable without jumping through some hoops (apple's server no longer signs off on the installation). It was a bug in the PDF renderer for safari, for anyone wondering.
Rooting iOS devices remains a hunt for exploits in every version release, and no one's ever sure if and when the next version's exploit will be released. Many 4S/iPad users on iOSv5.1 are have been stuck using a jailed, but perfectly secure device for months now, with no guarantee that the jailbreak will come anytime soon.
Each version makes iOS more and more secure, and there's no guarantee Apple won't eventually release a perfectly secure, jailed OS, and I hope at that point this OS dies off, but that may be asking too much.