No product is ever perfect, even Apple's wildly successful MacBook [1] line. A number of vocal MacBook owners have been experiencing annoying random shutdowns, and fortunately, according to Apple, a fix is finally at hand. MacBook SMC Firmware Update 1.1 [2] promises to fix the problem by adjusting the MacBook's internal monitoring system. Apple recommends the 417K download for all owners of MacBooks, even those units that have already gone through a repair process. You need to be running at least Mac OS X 10.4.7. And because this is a firmware update, remember to back up your data beforehand in case something goes wrong.
[1]: http://www.apple.com/macbook/
[2]: http://www.apple.com/support/downloads/macbooksmcfirmwareupdate11.html