Tablet computers--elegant slates that you operate with a touch screen--are attractive if you're a sci-fi fan. There's something functionally beautiful about a computer that's all screen and nothing else, and where your interaction is directly through that screen, not an intermediary like a keyboard or mouse. And the concept works great on smartphones.
But what you can do with a screen-only computer gets really limited when you expand the device beyond pocket size. There are two big limitations. First, you need a keyboard for doing real work. At least most people do. Perhaps a generation of kids will grow up that are as speedy on a virtual keyboard as they are on a real one, but until then anyone who does more than write quick e-mails and Twitter messages on a computer will want to take a keyboard with them. And typing on the screen, even if you can do it, is an ergo disaster. Either you have to keep your hands up in the air (if the computer is mounted vertically in front of you) or you have to hunch over your screen to see it. Maybe it's the national chiropractors association that's pushing this form factor. See also: Jeremy Toeman at Live Digitally.
While a tablet may be great for browsing the Web and viewing media, it's too big to replace a phone and too limited to carry around as a work computer. People will need their keyboarded Netbooks and notebooks for real work. Tablets, like other tweener devices, ultramobile PCs and Netbooks, are accessories to real computers. You can't do enough on them to justify the price, although they're sure nice to have if you have extra money for a gizmo that sits between your big computer and your phone, both in size and function.
So as an accessory, tablets are too expensive. If Apple releases a tablet in the rumored $700 to $800 price range, it will die. Not because people won't love it and lust for it, but because they won't be able to justify it.
I actually have higher hopes for the Crunchpad due to its Web focus and its lower price. But even then, at the rumored $400 price point, I still believe it's too dear for real human beings on a real budget, and it will reportedly lack local resources (storage) to make it a workable solution in a world of spotty connectivity (see also: Silicon Alley Insider). Geeks might like it, and buy them as living room couch Web-surfing computers, but for families looking to address real technology needs, a Netbook like a $200 Acer Aspire One offers a better bet: it has a real keyboard, its own storage, and you can take it on the road and do real work on it, like a notebook computer or a Netbook.
Of course, you'll probably be able to plug a keyboard into any of these yet-to-be-released tablets (see the Always Innovating tablet Netbook), but you'll pay extra for the hardware and it'll mean more gear to keep track of and prop up on your desk.
For specialized applications, tablet computers can and do work. The Aeryon spybot uses a tablet computer to control it. And in the consumer space, Amazon's Kindle, a tablet by form factor even though it has a vestigial keyboard, works because it but does things no other device can do at all: it can buy books instantly, almost anywhere, and display them on a screen nearly as easy to read as a printed page.
I love beautiful and elegant tech toys as much as any other geek, but geek love isn't enough to make a real market. Tablets need to cost a lot less and do a lot more before they establish a foothold in the consumer market.