The X-Series have for the most part have been solid machines. The obvious exception being some X61`s heating up on the left side of the palmrest.
This can be debated, but I don`t consider the X61`s heat not to be as big of an issue as the T61`s manufactured prior to August 2008 with an extremely high rate of failing Nvidia chipsets.
I`m also a big fan of IBM/Lenovo, Panny Toughbooks too. My latest Lenovo is a X230T and it`s been great, in my opinion, the best of the X Series by far.
If I was asked to choose between either the new T`s or W`s, give me the W please. Kind of a trick question though, because there was no wrong answer!
I don't have much knowledge in the X series, but that's good to hear that the X series are holding up. I think that the X series was started after Lenovo acquired the thinkpad line, that's why I didn't really know much about them. The W series are basically the same thing as the T series, just (a lot) more stuff packed inside. Regarding advanced video chipsets in laptops, they really shouldn't be there in the first place, haha. I agree though, the NVIDIA chipset is not too great in lenovos and I am not sure why it causes so many issues. It's still continuing to do so to a degree. They haven't really figured out too well when to enable the chipset when the user requires it, so it ends up running pretty poorly. I tend to have mine forced to run globally because I notice it does not turn on for some video games. :/