Originally Posted by Netspirit
I guess it is possible for a ball to go slightly downwards. If the pace is significant, it may be able to clear the net before it descends too much, and if the spin is significant, it may curve into the service box.
I definitely cannot serve like this - it probably requires a huge jump, racket head speed and arm extension. Recreational folks would be better off trying to hit twist serves by brushing up the left side of the ball, not down the right side.
Even leeD can hit twist serve around 100mph. There should be no problem for you.
Here is nice video of Marco Chiudinelli Twist (or Kick?) serve - http://www.youtube.com/watch?v=b8RGuB1Wj_E
I copied few frames from this video. Again optical illusion, it gives the impression the racquet moves faster than ball.
Figure 11. Marco Chiudinelli Twist Serve