Apple has just released iOS 4.3.4 through iTunes (4.2.9 for Verizon iPhone), which fixes the PDF exploit that allows JailbreakMe 3.0 to function, as well as providing bug fixes and improving stability.
Apple confirmed that they were working on the update last week. Apple describes the PDF exploit fix in a support document from their website.
Here are the direct links for iOS 4.3.4:
Also, iOS 4.2.9 has been updated for the Verizon iPhone, which you can download here.
Jailbreakers should stay away from this update until confirmation arises that there is a jailbreak available.