And another important point: There's a lot of momentum (possibly misguided, but it's there) toward "paperless" everything right now, but the problem is that you can't just draw all over a PDF. Rather, you <i>can</i> draw all over things, but it's super awkward with a mouse, and my pencil has a fantastic user interface that's hard to beat.<p>Tablets, though? Here's a device that promises to actually let me use my great UI (pen/pencil/stylus) to actually draw all over documents I want to edit. I think that <i>that</i>, together with the desire to go paperless, is going to be a big factor in wide adoption of tablets.
Why Tablets Will Fail:
They're too big to fit in your pocket. They're awkward to use in most normal situations (ie, sitting at a desk) They will require a case for screen protection. Perhaps a case that folds open -- kinda like a laptop. Current software is designed primarily for keyboard/mouse input. Using a software keyboard and a stylus offers very little to most users who type faster than they can write. (that's one of the reasons type writers were invented in the first place, who wants to regress at this point?)
Because of ergonomics, tablets will be more successful for content consumption type of activities like eBooks or entertainment, primarily on bed or sofa, but not at desk.<p>All input on touchscreen including innovative gestures still requires users to place their fingers directly onto their eyeballs: either with head looking down or with hands rising up. Both postures are not very productive for programming or desk jobs and can't sustain for long hours.<p>iPhone is more successful because of light weight and more sensors. To make tablets usage experience better, Internet tethering and sensor sharing via iPhone will help a lot.
The iPhone is essentially a small format tablet computer so I think the question of whether tablets can succeed has been answered. As to whether large format tablet can succeed, I think they'll be quite successful as a niche product but they really need to be pocket sized for everyone to carry one.
Tablets will only succeed when they have an OS designed around their features and limitations. Just mapping the touch screen to the mouse input and throwing on the latest version of Windows is not useful.
While I can understand the appeal of a tablet (heck I want one) it never ceases to crack me up when I think that what got me hooked on computers initially was that it didn't matter that my handwriting sucked.<p>I wonder how useful these devices would be when even I can barely read my script?