It drives me insane. I'm at work now and colleagues will say 'right, well I think I'll be off', and then they just sit there for absolutely ages.
I don't know why it annoys me so much but it really does. If you're going, go. Then there's an other hour while they slowly turn their computers off and slowly put their coats on.
It annoys me in the house too. 'I think I'll get off to bed'. And an hour later they're still sitting.
I know IABU, but my god, if you want to leave just leave. Don't draw it out over the course of a day.