I remember reading somewhere that the original script had him stuck in the same day for 10,000 years. It was clever of Harold Ramis to make it far fewer years so it works better as a story, but that original idea still gives me the shivers.
I watched it again with some American friends at Thanksgiving, and their children hadn't seen it. They were at college too, and I realised it had been made before they were born. That did make me feel old.