At the moment, I'm toting 3.6 pounds of happiness across South America, in the form of an old ebay'd Thinkpad X60. It was top of the line a few years back, with its 1.8ghz core duo. Now it's $350 off ebay, plus $100 total for a 320gb 7200rpm drive and 3GB ram to bring it up to the speed of the dev laptop that I was using just one year ago.
It took some getting used to to run the IDE in 1024x768 (12.1"), but at compile time the thing simply flies. And I know for a fact that my 17" Dell would have been monched a dozen times over on buses by now, assuming my back survived lugging the thing around for this long.
Give the X301 a few years to drop in price, and I'll pick one up as my next "disposable road machine."