Very very inconvenient. Writing on air is completely different and considerably more tricky that writing on paper. Physically more demanding too. It's one of those things that sound nice in theory, but not really practical.
But we can imagine a kind of ASL shorthand, like the original Palm Pilot's 'Graffiti'. Or, maybe if you buy two or three, you can set them up to combine perspectives, giving them more insight into the full 3d space.
That could be useful to deaf people and maybe could also serve as a new form of shorthand for people who are writing long texts on devices without keyboards.
You can even network more than one Leap device, to create even larger interaction areas.
I imagine two units orthogonal to each other might be enough to capture ASL.
-Chris
I don't see traditional writing being a realistic application, though perhaps cursive signatures could work.
However, I would make the good/bad list a bit more general: * good for manipulating UI elements that represent 3D * bad for manipulating UI elements that represent 2D
Maps and camera interactions (CAD) are perfect examples of things that represent 3D elements. Short games are another area that can represent 3D - longer games might also work well, but the user is likely to get tired of waving his/her arms around.
Much of what we do on computers today is strictly 2D. Coding, word processing, most web browsing, email, etc. Pencil tools/drawing tools are similarly usually just a 2D activity, so using a 3D-capable tool and reducing your movements to 2D doesn't really make sense.
good
* Fruit Ninja - made for single finger input, short gameplay
* Pinching and zooming maps - good because it's usually a short activity
* CAD camera interactions - good for periodic strange rotation needs or showing a client that doesn't understand the normal movement hotkeys
* Periodic writing with pencil tool
bad
* Shooters - can't turn player around, gameplay too long.
* Longterm writing or drawing - too tiring