I can't remember where I originally saw this idea. The best I could find through a Google search was this page (Scroll about half-way down the page.), and since I do subscribe to that magazine, that's probably where I saw it.
The idea is known as the "Captain's Log," and it makes use of the Notepad accessory that comes with Windows. On Windows XP, go to Start>All Programs>Accessories>Notepad. Open Notepad and type ".LOG" (without the quotation marks and in all caps) on the first line and then hit
Every time you open the file, the current date and time will be displayed on your document. Enter your documentation and save.