Let's do an experiment right now. If you have a laptop or a desktop screen in front of you, hold your hands out so your fingers touch your screen. Now hold that position for eight hours. No? Okay, try this: if you have a keyboard on the desk in front of you, look at it. Now watch that keyboard for eight hours straight. Any ergonomic position that's comfortable for your arms is not comfortable for your neck, and vice versa.
I use a Wacom tablet every day. There are things I can't do with the mouse anymore (like drawing clipping paths) because I've used a tablet for eight years now. Many say that a Mac tablet would be great for graphic designers. I say it's like my dream of driving the San Diego Trolley: it would be fun for about a half-hour, but then I'd get really tired of it. Having your hand-work area in the same place as your visual area would be frustrating to me, as my hands would be constantly in the way of what I'm looking at. Like most input devices, I like that keyboards, mice, and Wacom tablets be used without looking at them: critical for ergonomics.
Robert X. Cringely argues the opposite, saying if you just "give artists a big tablet screen to draw on" then Apple will at least break even on a tablet product. Not only is it insulting, but it's bull-effin'-puckey. Has Cringely even used a tablet to design something? Designers would all be at home in a week with neck-strain and RSI. Moreover, I'd reckon that without a keyboard, designers' ability to precisely control the position of objects (in software like Illustrator or InDesign, for example) would be seriously hamstrung.
I've also used a tablet PC before, which was frustrating. It had a stylus, which was okay, but the display was pressure-sensitive and not touch-sensitive. So precision movements with the stylus were nigh-on impossible. Typing using the stylus on an on-screen keyboard was ridiculous, unless I wanted to type like I was in third grade again.
Moreover, developers can't just "make" a touch version of "desktop" Mac OS X for fingers: objects like hit areas and UI shadows are entirely different, tweets Craig Hockenberry. The UI would have to become much larger, much different, or both. Trying to use something like Final Cut Pro with a tablet makes my brain hurt. The other option is to use a stylus, true: but Apple's current touch technology only works with fingers, toes, knuckles, and elbows so far.
Apple filed a patent last year about a huge, multitouch display area for MacBooks, but what's described in the patent ain't no tablet, but more like an Optimus keyboard. Nifty, I agree, but beside the point.
Steve himself just last year dismissed the idea of an Apple tablet, instead focusing on the soon-to-be-announced iPhone. He reportedly said that tablets appeal to a very limited audience (in the article, for example, the medical field). Technical limitations like screen density and wireless fidelity can be overcome. But without the backing of Apple's critical creative customers, will a tablet succeed?
I understand that for some users, having a computer to carry around in the crook of your arm has appeal. But is that group large enough for Apple to manufacture and sell Mac tablets in quantities that can make it money?