Why do some files in Mac OS X say 'Date Modified' as '24 January 1984 08:00'?
It is the Mac's birthday.

Jan. 24, 1984, was the date Jobs took to the stage to show off the very first Macintosh in a live demonstration. The presentation from Jobs stirred an audience of more than 3,000 people into a frenzy when the computer read aloud, "Hello, I'm Macintosh. It sure is great to get out of that bag."

http://appleinsider.com/articles/12/07/26/mountain_lion_easter_egg_references_debut_of_original_apple_macintosh