The answer as you probally know is it depends. All babies are different.
The basic guidelines ask the questions? is the child growing? Does the Child seem satisified? Is the Child having normal Bowl Movements? If Yes to all three then They are getting enough.
Some reference --
http://pediatrics.about.com/od/breastfeeding/a/milk_supply.htm
http://www.kellymom.com/bf/pumping/milkcalc.html
http://www.trixieupdate.com/archives/2004/06/2004_06_27_2303.php
http://www.breastfeeding.com/all_about/lawrence_anwers3.html