Good guide for those who are new to wii sports or just can't get it down
Just got a couple things to add
"The speed of the ball is simply determined by the speed that you swing your arm."
The speed is determined by how quickly the wii-mote goes from angle 1 to angle 2 (doing a shorter swing slowly could have the same effect as a longer more natural swing done quickly).
I've also noticed that releasing the ball sooner/lower results in a faster ball as well as more curve where as releasing high will result in a slower ball and little curve.