I've been using the same Lenovo X200 for four years and have been extremely happy with it. I'm running Linux on it these days after getting tired of dealing with Windows for the first year.

The display resolution has become a drag though (same 1366x768 as the x220). I love the portability and durability of this machine, but I've notice I tend to hack when plugged into an external monitor more over the last year rather than just using the laptop alone.

I've started eye-balling the X230, mainly because you can cram 16GB of ram into it. I would also consider looking at some of the newish T430s/T431s. Better displays, still under 4 lbs.If you buy a Thinkpad new, get the cheapest configuration you can and upgrade the memory (I've used crucial.com) and drop in an ssd yourself - you'll save hundreds of dollars.