Apple released a Mac OS X update this weekend called "The Networking Update." As the name implies, this update is designed to improve networking performance, specifically:
The Networking Update improves network and Internet access after restarting your computer or when waking from sleep.
You can get the update through the Software Update Control Panel in Mac OS X; the file is under 1 MB in size. As of this writing, Apple does not seem to have added this update to the support site at Apple.com.