I spent quite a bit of time with Microvision evaluating their Nomad device. It is an interesting technology.
It makes the background of the image clear, and all lines are then made red. Choice of red as that color doesn't appear often in nature, so there is less chance that when it is superimposed over the real world, that there won't be contrast.
It works currently at 800x600. With a Ce based touchpad for navigation and some arrow keys.
It does not work with servos. The technology they are using is proprietary. They are also working on HUDs for autos as well using same technology.
Same company produces the FlicScanner which is an inexpensive bluetooth optical barcode scanner that works great for kitchen inventory and DVD entry.