Unforunately i dropped out of University because i partied too much. I now have a great job working at a bank, have the weekends off which are spent partying / going out with friends. (i'm only 22, so i might as well enjoy it).
I do find it has negatively affected me...lack of sleep may also add to that. however if it was that bad i would just discontinue doing it. For now, i'm enjoying my twenties.
I plan to go back to school in about a year and i feel more ready then i was when i left three years ago as i've got my "partying years" out of the way and can focus on why i'm there: to get my BA.