Have you ever been in the middle of a movie and your phone starts ringing? I have, and it's totally embarrassing. Everyone is capable of forgetting to turn off their cell's ringer a time or two, whether it be in the theater, the office, or the courtroom. But with the Locale App for the Android G1, you'll never have to worry again.
With Locale, you can set up parameters that automatically change your phone's ringer to silent based on your location. Just enter addresses of places you don't want your phone to ring (either by entering the address manually, or using your GPS and map technology), and your smartypants cell will do the hard work for you. Locale is also great for remembering to turn your ringer back on after you've moved on to a different location, so you never miss an important call.