[karaterobot]

I'd have multi-touch be a sidebar in the textbook, but not a new section. Gestural interaction is not fundamentally different than a pointer device: it doesn't allow meaningful new behavior. It is sometimes a more intuitive way to afford the same behavior, though. I would agree that portable devices amount to a new paradigm in something—maybe UX—but not UI per se.

[zeroonetwothree]

It allows manipulations that are impossible with single touch (like a mouse). It’s pretty big for things like 3D manipulation.

[dlivingston]

You can do all of those multi-touch manipulations on a Macintosh trackpad (zoom, pan, rotate, scale, etc). However, that trackpad would still be categorized as a form of a mouse -- correctly, in my opinion.

All of these gestures can be (and are, given that 3D modeling is historically done on desktop) handled with a standard mouse using a combination of the scroll wheel and modifier keys.

[karaterobot]

Whether it's your fingers or an on-screen pointer, it's the same paradigm in the sense of it being the same model of interaction. You move a pointer around and activate controls on the screen by touching them. I'm not knocking gestural controls, just saying if I had to classify them, I'd say they're an evolution of the mouse or touchpad rather than a whole new model.

And they aren't an evolution in all aspects, either. Multi-touch controls are easier for some things, harder for others. Fine-grain manipulation, for example selecting cells on a spreadsheet, or playing an FPS video game, are harder with touch controls than with a device like a mouse. They've also got a size constraint (the size of your fingertip) that makes many interfaces harder to use.