It just depends on your destination. The US has no limit as long as you leave prior to the expiry date (or on the expiry date? I'm not sure).Not sure how much water this holds, but you might want to call your airline if your passport expires within 6 months. I remember hearing something that they won't let you fly if your passport is going to expire within the next 6 months.
The few minutes might save you a world of headache.