It really depends for me. It depends how bad the hangover is and how long I've been up for. Horrible hangover? No thanks. I'll stick to drinking my vitamin water and trying to sleep it off for the entire day...or two.
Mild to moderate one and I've already gotten up and rehydrated myself, had a chance to eat something, brush my teeth and now I'm just in that "ugh" feeling for the day...then yes, it helps.