I've always loved a window over the kitchen sink. My grandparents' house had one; my parents' house does, too. It's a wonderful detail that provides a pastime while doing the dishes. So, what to do when you find yourself (somehow!) in a home without a window above the sink? Try a mirror!
While it doesn't provide a view of the world outside, a mirror over the sink does bounce light around in much the same way as a glass windowpane (especially if there are windows opposite the mirror).
A mirror also creates the illusion of space in a very tiny kitchen and gives the visual interest of a framed view — that view just happens to be of yourself when you're doing the dishes!
What do you think? Would you find this a desirable replacement when you don't have a window over the sink?