1) Good question, I can't think of any off the top of my head. Maybe if you needed to snap photos of the Earth really quickly (and you had cameras that could take good photos considering the speed of the satellite relative to the Earth) it would make sense, but most imaging satellites are launched into polar orbits, meaning the orbit makes a right angle with the equator, or it's slightly prograde or slightly retrograde. Polar orbits ensure you can cover every bit of the globe.
I believe the reason Israel launches to retrograde orbits from its own launch sites is for safety concerns. There are a lot of inhabited areas underneath a trajectory for a rocket going to a prograde orbit, but for retrograde you just have the Mediterranean. Given high tensions in that region, launching prograde could easily be misinterpreted as an attack.
2) More power is required to launch into a retrograde orbit because you have to go against the Earth's rotation. When launching into a prograde orbit, the Earth's rotation gives you a little benefit, so you can use a little less propellant getting to orbit. For retrograde, you need to work against that boost, which, of course, requires more propellant.
It does not require more power to keep the satellite in retrograde orbit. Although I suppose if it's in a fairly low orbit it might be more affected by atmospheric drag since the relative velocity of the atmosphere against the satellite will be higher in a retrograde orbit, but I would venture to guess that the difference would not be significant, probably not even by one order of magnitude.
3) Yes, one of Saturn's moons orbits retrograde: http://en.wikipedia.org/wiki/Phoebe_(moon)#Orbital_characteristics