That's very good advice, and it isn't just our games that can behave badly when you start messing around with the system clock. Other applications depend upon an accurate system clock, such as anti-virus and security software, email applications, and many operating system functions. People have lost access to anti-virus updates as a result of changing their computer's clock.

I'd like to add that there are seemingly innocent things that people do on their computers that change the system clock without their realizing it. One very common way is clicking that handy little clock in the corner of the screen to check a date on the calendar. Before you know it, you've click OK and your system clock has been set to some other date in the past or future. It's easy to do, and you have to be careful.