My wife and I have a trio of hens, which net us about 18 eggs a week.  Our two kids (ages 1 and 3) go through heaps of eggs, and the ethics of mass-produced eggs and caged chickens were too much for me to take anymore.

Our house is on a quarter acre.  The backyard is probably a hair less than half of that, so maybe 1/10 acre?  We have a 4'x8' A-frame chicken tractor, which gets moved every 2 days or so.  Works great- keeps the litter from piling up, and gives them fresh ground to scratch and roll around in.