I'd really encourage you to try to spend a significant period of time using a Sony TX and then decide whether you could use one as your only computer.
Well, of course I would use it with an external monitor, keyboard and mouse at home. I'm using a 1.8 GHz G4 with no L3 cache on a 100 MHz bus, so such a computer should be faster than that.
The Asus S6 I'm talking about has a 2.5" hard disk and is better than the Sony. It doesn't have LED backlight, but it still weighs only 1.3 or 1.5 kg depending on the battery you put in.
There's a lighter Asus at 1 kg with LED backlight, but it uses a 1.8" hd, has worse gfx, and no gigabit ethernet or FireWire.