I'm a bit surprised that the Asus U36SD isn't in the comparison too; it's slightly lighter than the X1, although not quite as thin, has a better battery life with the integrated battery (and identical with the slice battery), the highest configuration has the same processor as the X1 (though I haven't found anywhere that actually sells that configuration), and a much better GPU.
The low-end configuration of the U36SD is about $400 cheaper than the low-end X1 or 13-inch Macbook Air, too, as well as having a better processor than both, although this comparison focuses on the high-end, so that's not too relevant.
The low-end configuration of the U36SD is about $400 cheaper than the low-end X1 or 13-inch Macbook Air, too, as well as having a better processor than both, although this comparison focuses on the high-end, so that's not too relevant.