Seconded. Worth looking on eBay for an X200s - it's arguably superior to the current X201. It was the superlight version of the x200, available with a 1440*900 display and had all sorts of carbon fibre bits and an ultra-low-voltage processor. With the 9-cell battery, you've got a machine that weighs under 1.5kg and will run for ten hours away from the mains. Randall Munroe has one - http://blog.xkcd.com/2009/06/12/laptop-update/

Unless you get a tablet, expect your Thinkpad to have a terrible screen with a cheap TN LCD panel. Newer Lenovo screens may have high resolutions, but contrast and color reproduction is awful. They are generally good quality machines otherwise, but the display could be a dealbreaker.

I have an x200. The screen isn't amazing but the build quality and warranty are incredible. I got the protection plan, managed to spill water/coffee on my laptop in two separate occasions nad had 90% of the parts on the laptop replaced within 3-4 days including shipping.

Be careful with video drivers... some of them are incompatible with Linux due to custom tweaks (such as 50hz monitors)