We agree on a lot of points. A medium-screen (3" to 4") GPS will live in the car. Using your phone for a second power-hungry function like a GPS receiver is a non-starter. My Garmin iQue3600 PDA/GPS was a reasonable combination for auto navigation and PDA but it's much bigger than I would want to carry as a phone (assuming it had cell capability added).
The other niche for standalone GPS units is in the field. When I'm hiking or backpacking, I need a GPS that will run all day and has replaceable (not rechargeable) batteries so on a multi-day trip, I can carry a handful of AA Lithium primary cells to keep the GPS going. (The newer field GPSs have the ability to load and use street/road maps and give turn-by-turn navigation as well, so that will kill my iQue soon.)
I agree that a tablet PC may supplant a dedicated ebook reader IF (big if) the battery life can be comparable. Ebook readers with passive (e-paper) monochrome displays will outlast any active/backlit PC display hands down. That's a technological limitation that will be overcome someday.
Tablet PCs are fine for pure graphical interaction but typing on a touchscreen keyboard simulacrum is a pain in the anatomy. Netbooks are a better lightweight alternative. (I agree that netbooks and notebooks occupy only slightly different levels in the same food chain.)
Finally, to everyone who builds a camera into a GPS, media player, netbook or cell phone, who cares? If I want a camera, I'm going to carry a REAL camera (Nikon D200 DSLR in my case). The camera in my cell phone never gets used and just adds to the cost, power drain and complexity of my phone. I literally couldn't get one WITHOUT a camera but it's the most useless appendage I can think of.
Interesting article, and you had me until you mentioned Tablets will exist between Smart Phones and Laptops. I think you have fallen into the hype of the iPad and are not listening to your own reasoning. Also, I am not sure why you think E-Readers will go away. No one is going to read a book on a Smart Phone and Laptops exist today yet E-Readers are doing really well. If you are going to replace something like a book, it is not going to be a do-all (yet nothing well) gadget like a Tablet. I think E-Readers will just get better leaving even less room for something like a Tablet.