Last year we started hatching Japanese Quails, good hatch rate (about 75%), managed to get the eggs cheap by buying about 4 or 5 dozen at a time.
But as said mortality it high, a lot seem to die off in stages as they get older. We managed to get a good number to layers, and had quite a few eggs from them. Unfortunately they all got killed by rats (only a couple were attacked, the others just scared themselves to death). A couple of other people I know said they had problems once the weather started getting cold, apparently they don't do so well. This year I'll be building a more sheltered unit for them, and will be trying again.
The eggs fetch a fair price, the birds sell well at auction, and really they are quite nice animals.