Name doesn't matter here, whatever you are calling them, it's a rectangular device with a screen in the front, and a processor, memory, storage, network chips...etc and a battery at the back. What I see here is really how to align the right set of features with the right form factors (Size, i.e. Screen size).
Category 1, iPhone/iPod Touch class Device. A multi media device with web and email functions. It is basically an entertainment tool. We have a few of these around already; some are doing better than few others in the block.
Category 2, a 'constructive tool' device, a tablet, you may call it. I believe this is where the future is heading. Aside from most of the entertainment features the smaller device has, it should deliver a set of much richer functionalities, without loosing the simplicity. The most obvious difference will be the use of the stylist, the pen. In the essence of the design, this device should be the perfect replacement of a personal notepad in the digital world.
So, why have we not got there?
It is mainly the processing power required is much greater than what was available in that form factor. This is about to change with the introduction of the new line of microchips from Intel, Atom. With Atom, it is possible to built a 'computer' with a size of B5 notebook, but as powerful as the main stream laptops in 2005.
The other obstacle is the software development, mostly the GUI design. To today, most of the sub-notebooks are running on full featured OSs. On a small screen, the user interface looks very uncomfortable. The EeePc is a good start, with its simple Linux GUI. It will be the direction of the OS development on such devices. But, don't forget the stylist, it will make a huge difference on the productivity of these tools.
The idea of the ModBook is not bad as an example, only to be too big in size. Imagine a tablet with 7" screen (3 iPhones together in a row), GUI similar to that of the iphone, but full-featured OSX running at the background. It will be able to running any software that you would install on your laptop, only to open in a new 'Space', meaning, only one application on the screen at a time, but you can always go back to the home to go to other program spaces. It will be so easy to catch the flash of ideas of yours.
These are just some wishful thinking, let's see what dishes they will bring to the table in June, when Atom is ready to be cooked.