Augmented Reality Apps, Anyone?

Andrew Parker and I recently wrote a post on the USV blog about “The Mobile Challenge” – looking for apps that make use of the unique capabilities of the latest (smart)phones to deliver experiences that were previously impossible.  Since writing that post, I have become fascinated with augmented reality apps, such as Wikitude by Mobilizy (Austria), Layar by sprxmobile (Netherlands) and Sekai Camera by Tonchidot (Japan).

I have no idea how well any of these actually perform, having only experienced them through Youtube videos, but they sure look like they might provide exactly the kind of unique experience we are looking for.   This leads me to two important questions: Has anyone actually tried one of these apps?  Also, are there any US-based companies working on augmented reality apps?