Yeah I commanded MobileMe to make noise on it and I literally stood in an alley at 5:30am listening for the sound but could not hear it. Have also sent a few dozen threatening messages with my Google Voice number added on in case they wanted to give up.
That's not going to work. If anything it'll just motivate the thief to get rid of the iPad by selling it ASAP since he knows you have remote access to it.
The best way to get it back is to use the same method and tell the thief that you're willing to pay $X as a reward if he calls and returns your iPad, no questions asked.