Discovered Tile today (via Daring Fireball). It's a small location-broadcasting fob that you attach to things you might misplace. An iOS app directs you to items within range, and includes an option to have the tile emit a chime to help you find it. When out of range of your iOS device, the system is designed to cloud-source the location from other tile users who may be nearby your missing item.
To truly appreciate the concept you need to watch the video (below) or visit the Tile website. It looks super-cool, and I've pre-ordered a few to give it a go.