We're inventing this stuff as we go, right now, which makes gestural and spatial interfaces an exciting thing to work on. Your broader point is definitely well taken. Touch is important. But touch, combined with free-space gesture, plus appropriate use of tools (like the keyboard), and voice, and head tracking, and other kinds of contextual sensing from our computers -- now that starts to look like the future.

I work at Oblong Industries. We're the folks who did the interfaces in Minority Report. We've been building gestural and spatial stuff for a long time.

Regarding (1) - standardization is really important. I'm old enough to remember the early days of mouse-driven interfaces. It took a long time for the standard window manipulation semantics, scrollbars, buttons, and drop-down menus to develop. The original Macintosh team did a lot of quite elegant heavy lifting in that regard. It's very much worth reading the stories on Andy Hertzfeld's site and in the related book. http://www.folklore.org/index.py ; http://www.amazon.com/Revolution-The-Valley-Insanely-Great/d...

If you'd like to experiment with a toolkit that provides a standard framework for building gestural, spatial, multi-screen, multi-device applications, please feel free check out our Greenhouse SDK. Greenhouse supports the Leap Motion controller, the Kinect, and a bunch of other forms of input. http://greenhouse.oblong.com/

Regarding (3) - we've got a lot of experience now with ergonomics of spatial interfaces. (We've been selling glove-based gestural systems to early adopter bigco customers since 2005.) It turns out that accuracy of the underlying sensing hardware is incredibly important, and then on top of that design of the gesture language is really important, too. Basically, if you have good enough sensing that small motions are precisely tracked, and then if you use that accuracy to track hand movements and poses that are "natural" (glossing over what "natural" means, for the moment), people can comfortably and happily use gestural interfaces all day, every day.

Think about it this way: most people "talk with their hands" all the time. (Some people wave their hands around more than others. But spend some time paying attention to people moving their hands while they talk; it's really interesting to watch.) Our high-end, glove-based systems track finger positions to 0.01 mm at 100hz. The tracking volume is big, so your motions aren't constrained. You can walk around and you can go right up to a screen or stand back from it. We recognize hand poses ("one finger point," "two finger point," etc.) "Talking" to the computer with your hands feels a lot like what you do when you use your hands while making a point in a discussion with another person. You don't get tired and you don't feel any strain or overuse pain.

The consumer-priced sensors like the Leap Motion and the Kinect don't yet provide this combination of tracking precision, tracking volume, and robustness to occlusion. But they're getting closer! And when a $50 sensor (or a few $0.50 sensors) give you the same accuracy and precision we have today with Oblong's optically tracked gloves, our collective expectations about interfaces and user experiences are going to radically change. (Or, more accurately, as happened with the invention of the GUI we use today, our expectations will change slowly over fifteen years, starting roughly now, with some moments of punctuated equilibrium analogous to the release of the Mac in 1984 and Windows 95 in, um, 1995.)