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I have used five (5) post IBM Thinkpad and the build quality has been absolutely fine and they mostly just work as you put it. And all of them have been reinstalled with Ubuntu at some point.
I recently bought a third generation Lenovo Thinkpad X1 Carbon. It had a very annoying fan, which made it unusable for me. It wasn't very loud, but it was a high-frequency sound which made it annoying. Eventually, I got myself a Lenovo Thinkpad T450 instead. So far this T450 has been very good. The fan almost never comes on. However, it should probably be noted that I got the T450 model with the slowest CPU. For thos…
Ubuntu 14.04 works like charm.
With an additional battery (the thick one), I can spend a whole day without electricity and the battery can be swapped without switching off the laptop.
It's so far the best ThinkPad that I had until now. I have the impression that at least with this one Lenovo improved a little bit the quality and usability.
The T440s was unusable - I sent it back after two days. The T430s was good, but flimsier and much heavier than the T450s.