I once ran into a Toshiba exec on an airplane who quietly showed me a gorgeous little subnotebook not yet released in the U.S.: the Libretto. For the next few years the only way to get a fully-functional PC that size -- half the size and weight of a notebook, running standard Windows programs -- was to fork out double the cost of a regular laptop for something like a Fujitsu Lifebook.
So Asus' hugely popular Eee subnote, which runs Vista, XP and Linux for $300, is a game changer. The machine itself is light and adorable, little bigger than a paperback. You could throw it into a backpack for an afternoon of surfing at a café without thinking twice. Sure, its 7" screen is a bit small. The original has wide black bezels on both sides, placeholders for the new model with a 10" screen.
But the real sticking point is the keyboard. With smaller keys than usual, it falls between thumb keyboards and full-size standard ones. I've spent some time typing on the Eee, and even when using only the tips of my fingers, it definitely crimped my typing speed.
Here's a possible solution. Back in Palm Pilot days, I used a full-size keyboard which folded into a 'w' shape and was little bigger than the Pilot in its carrying case. The Stowaway keyboard was comfortable, fast to type on and relatively cheap. On plenty of overseas trips, I took notes with the keyboard and my Palm V rather than bringing a full-size laptop.
Right now the barrier is that the 'w'-shaped Stowaway keyboard seems to come mainly with Bluetooth -- the USB version is hard to find -- and the Eee has to be hacked to support Bluetooth. Portable keyboards which support USB generally don't fold. The closest I've found so far is the Matias folding keyboard, which supports USB. Another option is the TabletKiosk USB folding keyboard, which is smaller because it omits the number pad.
But I still haven't found a 'w'-shaped USB keyboard which accordions into something tiny. So I'll probably track down a used USB Stowaway.
Eee User discusses this here and here.