I pulled a 16 hour stint on Skyrim when it first came out. Bought it on the friday, got it installed at about 2PM, and then started playing until 6AM. I took a few 3-4h naps after that, but by the time sunday night had rolled around I had put in 39 hours of played time.
Back when I used to play WoW, I had days where the course of action was:
Wake up -> Log in -> Check auctions -> get coffee -> play -> get breakfast -> play -> bio -> play -> find snacks -> play -> ............ -> play until head hits desk and you get logged out for inactivity.
I've also had a marathon playthrough of MGS4 with my friends. We really enjoyed all of the games, so when it was released one of my friends who was out of town visited for the weekend. We finished the game in about 42 hours (got stuck on one of the boss fights not really knowing what to do).