I did a rough calculation on how many manicures a bottle of polish contains. I think there are around 50 manicures in a regular nail polish bottle, like a full-size OPI, Orly, Chanel or Essie. That is if you use two coats of polish every time you paint your tips.
This means you have to paint your nails with the same polish once a week during one year’s time to finish up a bottle. Personally, I’d rather have my hands forever “naked” than wear the same color all the time. Thus, I’ll probably never use up most of my polishes!
But then again, I’m not aiming to ever finish up my make-up products. I only buy the stuff I really like, but still, newer, better products come my way, and I just leave the old behind.