It can really depend..
If there are other seats around, you can be sure i'm not movin'. I work good 10 hour days at times and i'm fried when i hop on the subway to go home. I'll be damned if i'm standing for anyone until it's my stop. Usually though, at that time the subway is not really full of people and it's not so much of a problem.

What really gets me though are the people that put their bags on the 2nd seat beside them and don't let anyone else sit there.

Rush hour = 1 seat per person. Not 1 seat for you and 1 seat for your belongings.