There's really three different functions here:
1) Remote going backwards and forwards. As far as I can tell, when you do this, it will straighten the wheels, but won't turn the car to avoid walls. I might be wrong about this. This is useful, obviously, for getting into and out of really narrow garages and parking spaces. Otherwise it's just a party trick.
2) Automatic parallel parking. This actually seems to work really well. However, the hill in front of my house is too steep. The car actually says it won't do it because the hill is too steep. When I tried it on flat ground, it parked perfectly.
3) Automatic straight in parking. Kinda useless. And scary. I would only use this while standing outside the car so I could watch the corners, and even then, the car seems to need a lot of steps to park itself. It's a lot easier to back the car in myself -- aided by all the camera views.