Don't call me Chicken

I have been thinking about keeping a couple of hens for eggs. Nothing too fancy, just a couple of friendly old girls that will see me right for my morning boiled egg and soldiers. I've bought the books, read the manuals and learned how good keeping chickens can be. But there has to be a downside too. Will they fly (or flap) away? Will next door's cat get them? What about foxes? Isn't cleaning them out a pain etc. So please help me - why shouldn't I keep hens?