Glad to see someone else who is interested in AR! I highly suggest you watch the anime Denno Coil, I think it's a great example of an AR environment. I'm serious, you really should watch it, it's great for inspiration.
Also, I'm looking forward to the glasses featured in this article:
http://spectrum.ieee.org/tech-talk/at-work/innovation/finally-an-augmented-reality-i-can-stomachFrom what I can tell, this is one of the first 'good' AR glasses that a consumer might be able to get.
As far as the ARToolkit goes, I've wanted to use it, but I lack a good webcam to really use it with. The coolest thing I've seen done with it was where someone made the glyphs tools. One of them was a cursor, you could grab virtual objects with it and move them around. The other ones allowed you to scale/rotate objects when you linked them to each other.