I think we've set a new PHP release record today, 3 releases in one day, PHP 5.1.5, 4.4.4 and 5.2.0RC2. The first two are aimed at addressing a series of security faults that were discovered in stable branches.
The good thing is that the issues found are mostly local exploits, so upgrading should definitely be a priority to shared hosting providers or multi-user PHP systems. That said, I would still recommend that all users of PHP consider upgrading their installs to the relevant releases. For information about the exploits themselves go to php.net
He links to the downloads of these two new versions and includes more about the latest release candidate for HPP 5.2.0 - RC2. They're shooting for a final release of 5.2.0 sometime in September and asks that anyone and everyone out there help to test the code on their systems to ensure a faster, cleaner result when the final code comes around.