'Traditional tablet PC' can't mean passive digitiser (dumb screen that you can touch with a stylus or a fingernail), because those are limited to industrial tablets and PDAs, and very few of them are PCs rather than embedded OS devices (Win CE and embedded Linux for the most part). The OQO and the Nokia 770 are the main exceptions (Windows XP and a reasonably standard Linux) and they're PDA size. You do need a virtual keyboard on most passive digitisers because of the poor smoothness; even when the OS lets you write anywhere on the screen, the curves of your writing aren't what they should be.
But the modern Tablet PC running the Tablet Edition of Windows XP is a bit of a different beast. The active digitiser samples more often than a graphics tablet (though it's the same technology, just a higher sampling rate), so it's very like writing with an ink pen. The only time you'll hunt and peck on a virtual keyboard is for passwords and URLs where 'usually right' isn't good enough. The rest of the time it's up to the application developer whether you write into an input strip - or anywhere on the page.
OneNote, Journal, Art Rage, Grafigo: applications that are designed to work on a touchscreen let you use the screen without needing to go back to a keyboard (virtual or not). Utilities like Sensiva Symbol Commander and ActiveWords let you trigger actions with gestures or individual letters instead of keyboard shortcuts. ritePen is a great handwriting recogniser for desktop and Tablet PCs that lets you write anywhere, even if the application isn't designed that way. A video editing or musical composition app that understands pen input shouldn't need the keyboard input that's designed to be faster than mousing through menus when your input with a pen is both fast and accurate. The next generation of touchscreens won't have the alignment issues that have made it hard to recogise input close to the very edges of the screen (which is why Word's write anywhere option doesn't cover quite all of the screen).
'careful integration'. Definitely important.
'responsive software'. Absolutely.
'eating up screen real estate'. Not when you design and integrate it well. Touchscreens aren't the problem; it's understanding how to use them to replace the keyboard rather than replicating the mouse.
This is another place where I'm impatient for Vista; it will have a cross-hair cursor to make it obvious you’re using the pen, on-screen ripples that let you know you’ve clicked on the screen and eight gestures called flicks that mean you can copy, paste, undo and delete just by flicking the pen in a particular direction. Vista can also learn what your handwriting looks like to make it easier to recognise what you write. If you want to use your finger to touch the screen to select something and it's a combined active and passive digitiser so you can, there will be a little magnifying ring to show you more clearly where you're clicking.
As to the form factors, the first is very like the Fujitsu Siemens Lifebook with touchscreen sitting on my desk at the moment. Folding the screen down to use it without the keyboard is the principle used by any convertible Tablet PC, although I can't see room on the mockup for any hinges ;-) And yes, narrow widescreen is a little off when you rotate it to portrait. This falls in what Ken Delaney at Gartner told me he calls “the 1kg wasteland” because so many products of this size and weight have failed, compared to standard notebooks or smartphones and PDAs. “You don’t have the benefits of the larger devices or the portability of the smaller devices”.
The notebook using a second screen as a configurable keyboard looks huge fun. OLED would do that nicely. It would, as the blog remarks, be pricey. It's price that's held people back from buying devices like Wacom's Cintiq (a touscreen monitor that's a desktop Tablet PC) because everyone one I know who's seen one wants one but not enough to pay that much. And I don't think a screen would be comfy to use for typing - with no key action your fingers get tired very quickly on projection keyboards. We've been using pen and paper for centuries and we're good at it. Making software as good at it shouldn't take that long.