I was looking at the response headers for my GMail account and noticed that the date Fri, 01 Jan 1990 00:00:00 GMT shows up as the value for "Expires" over and over again. I suppose this is just an easy constant to make sure the browser understands this is past its freshness date. But is there any significance to that particular date? One might as easily have used the same date in 2000, or 1970, or whatever. It's not quirky enough to be someone's birthday or date of college graduation or anything personal like that. Maybe it's just arbitrary, but I was wondering if someone has a good explanation why that particular date was chosen.