Augmented-Reality (like that featured in my future of timekeeping concept) is making some progress.

The "magic lens metaphor" was recently demonstrated to good effect on PDA class devices... Mass market opportunities are sure to follow via cameraphones. We should expect a windfall of innovation as a result, not the least of which includes a location-aware "spatial internet."

Below: A virtual train appears properly superimposed onto the image of real train tracks as seen by the camera:


Thanks Gizmodo