When Jeff Goldblum first opens his computer and shows the president how much time is remaing before the aliems attack, the countdown on the computer says "remaining time". Later on, when Jeff Goldblum, the president, and other characters are on Air Force One awaiting take off, Jeff Goldblum opens his computer and the countdown on the computer now says "time remaining".
I also loved the part where, although not really a slip-up, Will and Jeff fly to the alien mother ship and connect their computer to the alien's computer to download the virus... WOW! I mean holy gees, I can barely connect to the internet without problems, let alone an alien civilization.