How long can you grind?

I'm curious to know how long people can grind before getting bored. And what keeps you motivated to grind?

I used to be able to grind for hours years ago, getting 7% on my f/p mage at lev 6x but now training is like... ugh

my longest session is 22hours. it was on a bishop what kept me going is talking to my buddy list and on msn the entire time also music helps