It's a simple idea really. Make it easy for anyone at your home to pull out an iDevice and play what's on it over your audio system without having to fiddle with cables and the proper connectors and then a compatible USB port. Some products, such as the Musical Fidelity M1SDAC have this already built in, but if you don't have it, here's an easy way to add it.
The $249 rBlink gives you the ability to connect any Bluetooth device like an iPhone wirelessly to the system. Plug the rBlink into an extra input on your stereo, and then have the Bluetooth enabled iDevice add it from their menu. Maybe not the best sound in the world (though better than it used to be with Bluetooth), but easy for your pals and great fun at parties.