The system works fairly well here in Atlanta. I have a Galaxy Nexus on Verizon and when the alerts come in it buzzes and it's quite loud with it's own alert tone similar to the one you hear during emergency broadcasts. The message appears over the lock screen and the screen automatically turns on for about 2 minutes.My wife has an iPhone on Sprint and gets very similar alerts at the same time mine does. We've noticed that if I'm at work 30 miles away she may get a message and I won't so the geographical locating is pretty good. While I have seen it for Amber alerts they most frequently use it for tornado warnings and flash floods. Both of which Atlanta gets a lot of each year and a recent one gave me enough warning to seek shelter when a tornado was spotted so I welcome the system and hope they get the bugs out in other areas of the country.
Criminals rejoice! No longer do you have to randomly break in to houses to see what there is to steal. There's now an app to tell you exactly which houses to rob.
But it does move! -- Galileo Galilei