Yup, I have left before. Twice.
First time was a combination of time restraints and horrible connects. I was on dial-up, and it wasn't cutting it.
Second time was connects again. I was on ISDN, and it too began to sour.
I am now on cable, and don't have anything to complain about- other than time, which is still a problem that makes me consider dropping the account from time-to-time.