I'm still not convinced that tablets will be popular in the near future. The current paradigm of tablet PCs–make the screen touch sensitive and chop off the keyboard–has major ergonomic and usability problems. How do you hold it for more than 5 minutes? How do you input text without it being a complete chore? The software and hardware will require radical changes to solve these problems. Maybe Apple has thought of something, but a big iPod Touch won't work.
Voice recognition isn't viable either. Do people really want to talk to these machines all day–in offices, subways, coffee shops? Doubtful.
I think people who believe tablets are going to replace the PC are missing the point. One of the big concepts we're building at my work is the idea of devices that are designed around limited input scenarios.
In other words we believe there's room for two types of devices: Viewing devices with limited input (like tablets) and input devices (like PCs)
To give a personal example the most obvious usage case here is the e-book. If you could have every book you've ever owned at the touch of your finger that would be worth something even if you were limited to basic input on the device. Now combine e-books with all your movies and music and you start to see how there's room for devices with limited input.
(For the record we've been using ELO Touch Screens to test usage scenarios until the perfect tablet shows up)
You make some good points. I think there is some niche potential for tablet devices--hospitals, drawing, books (as you mentioned).
On the other hand, e-book readers have found success by doing things laptops can't, like lasting for a week on a charge, being legible in bright sunlight, and being extremely lightweight. I don't see the same happening for movies (laptops are better for movies since you don't have to hold them up) or music (iPhone/Android wins for that).
Also, e-book readers are replacing books, so while you're carrying another device around, it's probably a net reduction in size and weight for most people.
Here's a concept that would sell like hotcakes: Laptop with a dual mode LCD/e-ink 10", touch-sensitive, swivel display that can be held like a tablet, 24hr (or more) battery life, half-inch thick and less than a pound. Not sure if it's technically possible right now, and I'm sure it'd be quite expensive if it is, but when such a device becomes widely affordable, these niche tablet/e-book use-cases would just be part of your laptop.
Larger tablets (i.e. beyond the iPhone size) work just fine with handwriting recognition, it's worked great for over 10 years now. Sure, you need a stylus rather than a finger, but again on a larger tablet, finding a couple of mm for a stylus holder is easy, and you can fall back to virtual keyboard for short-duty entry where a stylus is impractical.
When I used to use handwriting recognition - back about when OSX first came out, I found it to be far more comfortable than typing, and I'm a fairly decent touch-typist (~100wpm).
Voice recognition isn't viable either. Do people really want to talk to these machines all day–in offices, subways, coffee shops? Doubtful.