Ever since Apple killed the Griffin IR remote on the original iPod I've been wanting to consolidate my iPod with a home theater remote. The iPhone seems perfect for this; with an infinitely variable canvas available, you could theoretically do anything with your remote.
The trouble is getting an IR signal to your components. The UnityRemote from Gear4 solves this problem by connecting your iPhone to a small cylindrical IR beamer via Bluetooth. We didn't get much of a chance to try it ourselves, but the demo was mighty impressive. I should note that Gear4 is not new to this game -- they created an