Technical Limitations to Wearable Eyeglass Monitors?

fprintf asks: "What is the technical limitation that is holding up wearable eyeglass monitors? It would seem to me that we have had miniature color viewfinders on Camcorders for quite some time, and with LCDs getting ever cheaper, what am I missing? I know there is quite a bit of interest in head and finger mounted pointing devices, but to me getting rid of that big monitor and strapping on a headset w/ the possible 3D implications would be wonderful. How about a GUI on an OS that supports Width and Height, but also depth?" It would be interesting to know how far wearable display technology has progressed in the past couple of years. Replacing the traditional goggles with (something closer to) a pair of eyeglasses will be a pleasant milestone for those Wearable Computing community.