There might be a Unity / Webcam problem with the new Macbook Air:

http://forum.unity3d.com/threads/187288-WebCamTexture-devices-Length-returning-0-for-new-MacBook-Air

...presumably it's the new one you have right?

N

DavidBeard wrote:

Do you have a Unity Pro license, which is required for the Web Cam feature to work - and if so, are you seeing any errors or warnings in the WebCamBehaviour panel in the Inspector?

Yes, I have Unity Pro. The webcam on my macbook air (10.8.4) definitely works - in the browser and using other apps. However, the AR Cam error in inspector reads: "No camera connected!" 

Do you have a Unity Pro license, which is required for the Web Cam feature to work - and if so, are you seeing any errors or warnings in the WebCamBehaviour panel in the Inspector?