I had my cat taken out a few weeks back. the sound to me is more mature, before when i passed the 5000rpm, the car went into a whining sound.
As far as power increase. well, first i dint feel any diffrence, but now, i think the torque is a little cleaner from 2000-4000rpm..may be is wish ful thinking. it cost me $30 and 1 hour to get it done.