Over the past 48 to 72 hours, Apple has issued a lot of updates, for everything from AirPort to RAW support.
I just ran Repair Disk Permissions on a couple of Macs that have gotten all those updates beamed down… and there were quite a few permissions glitches.
So, be sure to run Repair Disk Permissions (from Disk Utility) after running the update.
While Leopard has improved in this regard, I still suggest running Disk Permissions after any update that requires a system reboot.