Back when I started using windows 2000 there was a bug where the copy time would literally read random numbers from hundreds to thousands of days as you copied something across the network. This was especially true for files greater than 2GB. The progress bar would be the only correct indicator of how long the copy would actually take. I haven't seen it popup in my Windows XP wanderings, but here it is again in the newest most stable version of windows yet.

My Arse. This was on Windows Vista Home Premium of wireless G to a wired samba server.