You know, it has always driven me crazy that iCal shows a date of July 17 when it’s not running – yet shows the correct date when it is running. Given the confusion some ex-Windows users feel over the Mac interface to begin with (often not realizing that a program typically continues to run after they close its window) this can make things even worse.
A friend of mine got a PowerBook around July, and inadvertently wrote the date of July 17th on correspondence for several days before realizing what was happening!