Yeah, I think going overborad is the main concern here...once in a while is one thing, but for those of us who are prone to abuse (alcohol or other), it can be a problem.
The main thing of course is focus, which at times can be nothing but cumbersome. So on those bad nights, as some of the others have said, diet cola, even better caffiene free diet cola (saves some of us from our kidney problems) will help. Of course, poundin' the alcohol everyday is only going to kill you, but if you keep things in perspective, like our 'once a week' (or maybe more, depends) cheat days with food, you can still lead a healthy life.
As long as you don't go crazy with it, a night here and there isn't gonna derail you from your goals. As long as the day after isn't a hangover-filled puke fest; just work the shit off and keep growin'!!