Apple released an update to Safari 4.0 Wednesday, version 4.0.1. The release notes said that the update, "addresses incompatibilities between Safari 4.0 and certain features in iPhoto '09, including Places and FaceBook publishing."
The download weighs in at 43.8MB for Intel Macs, and can be accessed through Software Update. Windows users can find it through the Apple Updater app. Installing the update requires a reboot.
As of this writing, the update has not been added to Apple's Downloads page, but we expect it to appear shortly.