Apple released MacBook Pro SMC Firmware Update 1.3 on Thursday. According to Apple's release notes, the update "adjusts the fan behavior in MacBook Pro systems (15-inch and 17-inch) when running under high workload conditions."
Like other firmware updaters, MacBook Pro SMC Firmware Updater 1.3 installs as an application in /Applications/Utilities. The application must be launched before the update process will complete.
The update requires Mac OS X 10.4.11 or 10.5.7. It is free and available via Apple's Software Update application, or as a downloadable installer from the Apple Support Web site.