Reminds me of a story about Y2K compatibility testing:
There was this all-Mac shop that wanted to verify their Y2K compatibility, so they set their network time server ahead to January 2000 to see what would happen. Everything seemed to work fine, but then they noticed the network running sluggishly. They traced a bunch of extra network activity... turns out that their ancient Mac II backup server thought (the clock having been moved forward) that it was way behind on its backup schedule and started doing daily/weekly/monthly/yearly back-ups!