Apple has acknowledged the fact that some MacBook users may be experiencing intermittent shutdown issues with their machines.
A small minority of users have been experiencing the 'intermittent shutdown' issue, whereby their machines simply turn off for no apparent reason at sporadic intervals. While Apple had previously taken its normal stance of refusing to acknowledge the problem, they have now created a knowledge base article urging users experiencing these problems to contact AppleCare.
Disgruntled MacBook users have created the website MacbookRandomShutdown.com to share their experiences of this problem. It's possible that the creation of this website is what prompted Apple to acknowledge the problem.