I think that they should be illegle, but I would also like to have one.
If I had one, I would not walk into a resturant or theater and turn it on. Instead, I would carry it and If some one was using their cell phone obnoxously, then turn it on.
Yesterday, on Vday, I took my wife out to dinner. While dining, 3-4 people recieved or made cell phone calls. Only one of these bothered me. The man recieving it had to stand up and virtually yell into his phone. I personally think he was trying to be noticed. He was, and would have been a perfect target to have been jammed.
Just my opinion.