Yes, you can add cuve/spin to the ball, but as the back wall gets further away and the balls speed up, the effectiveness of it drops. It's really only usefull at times when you're trying to keep a ball from passing by the front screen and curve it back inside the field.
When looking at the highscores it seems as if most people don't understand the concept very well, this is probably related to my attempt at a short explanation (players hate reading). I get scores of well under 500 pts while you can get 500 points in only 10 bounces with 1 ball (1050 pts in 14 bounces), if you manage to avoid the sides that is.
I show a brief explanation after loading the game, but it seems it's unsuccesfull in communicating this concept.
Any ideas for a better worded description are very welcome, I'm not a native english speaker, so I'm not entirely sure about the effectivenes.