-when you've memorized everyones bio word for word.
-you find yourself talking about the game to all your friends.
-you stop whatever your doing and begin searching for a computer because you can sense a new game day has come.
I have a shinobi sense for that last one, like 3am this morning. I was playing Elder scrolls then paused the game and came down stairs to get on the computer
It develops as you play the game. Every morning if I'm feeling crap it means the new day has started and I overslept.
If i feel great it means theres plenty of time to catch the morning gameday.
And if I feel really crap it means its 4:00 and I've overslept 2 gamedays.
Its kind of worrying in a way.