I think the neatest feature is that it will trigger a noise even if it is in silent mode. There is nothing worse than wasting 15 minutes searching the house for a vibration when you know the phone is there and you can hear it ring on the other end. Of course, this largest problem that this doesn't solve is that you must have service or it doesn't work, and for GPS to work well, you also usually need a clear view of the skys, especially on a cheap cell phone GPS.

Another service I can recommend is phonemyphone.com, which lets you enter a phone number online and it will call that number so many times until you find your phone and pick up.