Vinylogous' excellent contribution is up at Not The Lab. A key excerpt:
Quitting grad school is a really taboo subject--maybe even more so than mental health or the fact that academia is pretty rubbish at drug discovery. Why don't we talk about it more? Grad school should not be the only priority in one's life--and it's perfectly OK for it not to be the highest priority (although certain PIs may disagree).
Go over there and read -- it's very good and worth your while.