Theres one in town where I live, its mildly annoying, but no one pays any attention to it.
Especially not me, because I have tinitus so i can hear a high pitched sound most of the time anyway.
I would argue that the people that these devices effect properly are those that suffer serious autism (No I dont mean dislexic, I mean proper problems Like AS and such) as these people are often more sensitive to high pitched sounds and can also find it to be quite painful or uncomfortable. (My older brother Has got AS and so has one of my friends, my mum also works in a special needs school)
"Yobs", despite being of low intelligence, don't find the sound painfull, or uncomfortable but just irritating, and you still see kids hanging around outside where these things are.
Having said that, the ones I've seen are always on, so they may be weaker then the temporary ones.
How about arming shop keepers and fire engines with tear gas ![Big Smile [:D]](/emoticons/emotion-2.gif)

TBPITW 13-14th Sept 08