I stumbled across a small one in The Curse of Monkey Island a long time ago. I had gotten it for Christmas and was playing it the day of new years eve. I'd forgotten to turn off the computer earlier that evening, so after I came in from watching the fireworks I went in to shut down the game. I remember that I'd been impressed with the in-game clock (on a tower) that was in sync with the real world, and where Guybrush would voice the time like a telephone-time-service. Imagine my surprise when I ended a conversation with a character (don't remember which one, but it was near the clock tower - maybe at the dueling grounds) and after his usual reply he added a "... Oh - and happy new year!"
