There is a lot of masking involved, and it's a pain, but big sheets of cardboard from packing cases are ideal. The better sprays have a 10-inch fan which is fairly tight and accurate, so masking doesn't have to cover an entire window.
I've seen Earthborn paints applied with a spray and it has worked well, although spraying a diluted paint does tend to show up the slightest defect in the surface being painted, and is far less forgiving than brushing on the regular stuff. It's also something with a bit of a knack to it - the chap who sprayed the walls on a house I was doing up had a rather spatter-filled learning curve before he mastered the technique.