In the great big gap between the laptop computer and the smart phone, there's a device that just never seems to quite take off: the tablet. 
Last week while visiting the University of Missouri, I bumped into Roger Fidler, who's been stumping for the concept since long before it was technically possible. In fact, for a long time he carried around a wooden mockup, with a fake newspaper image pasted in the imaginary window, to demonstrate the concept of an electronic tablet newspaper.
The technology is here today -- sort of. Fidler briefly showed me the iRex Iliad, a low-power device based on "electronic ink" display. At a recent trade fair in China, Intel rolled out a new vision of a "mobile internet device" powered by Linux and sporting a user interface curiously similar to that of Apple's iPhone, which supposedly is coming next month. And Nokia's 770 Internet Tablet wifi device is sitting on display at my local CompUSA.
Is this finally going to be the year of the Web pad? I don't think we're there yet, and we may never get there at all. It seems to me that all of these devices have struggled with a common set of issues over the years, and have only partially solved them. They include:
Special-purpose assumptions. If a device is only good for one purpose -- say, reading electronic books, like RCA's failed devices of a few years ago -- it's hard for many people to justify carrying it around, much less shelling out many hundreds of dollars. Computer technology can do all sorts of things. My phone plays MP3s and lets me read my email. My laptop lets me call anywhere on the planet using Skype. We don't want to eat with a Swiss Army knife, but some flexible multipurpose tools can be mighty convenient. If something is going to be a specialty item, there should be a big payback, like the iPod's ultraportability.
Lack of content. The obvious market for an e-book reader is the overburdened student whose back is being permanently disfigured by a hundred pounds of clay-coated paper bound into textbooks. But the content isn't available and our schools are having enough trouble upgrading to conventional books printed in this century.
Lack of connectivity. In the pre-wifi world these devices were designed to be loaded with content at home, then used on the road. But anyone with broadband knows the real magic is in the net. Today you can get free wireless at the corner Taco Bell, so the "tablet" is being re-visioned as a Web appliance.
Read-only assumptions. All the early devices struggled with input, if they bothered to try at all, and the problem has only been partially solved with touchscreens, "soft keyboards," handwriting recognition, and the like.
Poor functionality, bad UI. The Belgian newspaper De Tijd ran a test last year, giving a couple of hundred newspaper readers an iRex reader. Among the findings: Users were irritated by the slow performance (a result of battery-saving techniques such as the E.Ink display and low-power CPU) and struggled with network configurations. I never touched one of Microsoft's Origami devices, a notable failure, but I would expect their UI to be as generally crappy as everything else they do. Consumers want products that just work, like the Tivo or the iPod.
Form factor. This is the toughest nut to crack. Not big enough to be a laptop, not small enough to be a phone, the tablet struggles to fit in. Is five inches too narrow? Is seven inches too wide? Should it be a landscape display, or a portrait display? Should it pretend to be a computer (like Windows CE) or something else entirely (like iPhone)? We are no closer to settling these questions today than when John Sculley was pushing the Apple Newton.