Apple yesterday released MacBook SMC Firmware Update 1.1 which "improves the MacBook's internal monitoring system and addresses issues with unexpected shutdowns." The update was released to address RSS or Random Shutdown Syndrome that has plagued MacBook owners.
You must be running Mac OS 10.4.7 or 10.4.8 to install SMC Firmware Update 1.1. If you're running the required version of the OS the update will appear in Software update, alternatively you can download it directly from Apple (<1MB). The update is recommended for all MacBook systems, including those that received warranty repair.
The MacBook RSS problem surfaced in August 2006 and a Web site was set up by affected consumers to track the problem. In September the RSS problem was believed to be a design flaw in the heat sink. Around the same time Apple has posted a one-sentence knowledge base article on the topic that simply said "If your MacBook is shutting down intermittently, please contact AppleCare for service."
Some MacBooks sent in to AppleCare for repair received new processor heat sinks while others recieved new logic boards. Many users still reported RSS problems after the fixes.
The infamous one-line kbase article was updated yesterday with information and links to MacBook SMC Firmware Update v1.1.