Apple on Wednesday released a update to iOS for both the iPhone (4.0.2) and iPad (3.2.2) that plugs the vulnerability that allowed the JailBreakMe jailbreak to work.
There needs to be some sort of vulnerability in order for a jailbreak to be created for a version of the iOS. In this case, however, the vulnerability found was a flaw in the way the Safari browser handled PDFs. It's a minor update, and quick to install, as we discovered when we tried it out.
Jailbreakers (and they should already know) should probably eschew the update until after a new jailbreak is created. Those users would (should) already have installed the protective workaround
for jailbroken devices. There is also talk of a patch
for jailbroken devices, as the work involved in jailbreaking a new OS version is probably more than that involved in a patch.