In the SignOut method of System.Web.Security.FormsAuthentication, the ASP.NET team chose to expire the FormsAuth cookie by setting the expiration date to "Oct 12 1999".

HttpCookie cookie = new HttpCookie(FormsCookieName, str);
cookie.HttpOnly = true;
cookie.Path = _FormsCookiePath;
cookie.Expires = new DateTime(0x7cf, 10, 12);

What's the significance of October 12th, 1999? Is it an inside joke, or is there some valid reason to set your cookie expiration to that particular date?

Edit: The theories below are interesting, but they are just guesses. Since Phil, Scott, and other members of the ASP.NET team are on StackOverflow, I thought it would be fun to offer a bounty. Hopefully someone can track down the original developer and get an authoritative answer.

Awarded: To Scott Hanselman for escalating this one all the way to ScottGu. I was really hoping for some sort of super-secret, Illuminati-esque meaning, but looks like it was just the old "one year ago" trick.