Easily the most useful gadget I've ever bought for my bike. Commuting to and from school in NYC, it sees daily use, especially since a good number of pedestrians cross against the light, or in the middle of the street without looking for whats coming first, and a lot of drivers have a bad habit of checking their mirrors after they've already started turning.
Also extremely effective at clearing pigeons on the road, which aren't always afraid of people.
The only problem that I've had with it is that in dusty conditions, dirt can find its way inside and prevent the diaphragm from vibrating properly, which is most likely the problem that Narwhal was having. But this is why the cover over the diaphragm can be unscrewed and the dirt cleaned out. I usually have to do that after about a month of normal use.