I have owned several T (& W for work) series Thinkpads starting with the IBM T21. I am very satisfied with them, and I plan to replace my current T400 next year with a T440. I have ran Linux pretty much exclusively on the T line (early Fedora Cores and eventually Gentoo since 2004 on the T21, exclusively Gentoo now), and because they use mostly Intel parts, I have never had much trouble getting everything to work.
The features that keep me coming back are:
Availability of decent resolution (1440x900) matte displays
The ultrabay (can be used for an optical drive, second battery, or second disk drive)
The build quality and user replaceable parts.
I got my current laptop from their outlet as a lease return. It didn't include Windows (actually shipped with Free DOS). I immediately bumped the RAM to 8GB, added a SSD, put the original HDD in the ultra bay, and it's been going strong ever since. I have had to replace the keyboard (spilled some aged vinegar on one it), but other than that no problems. I am only thinking of replacing it next year to move to a quicker processor and more RAM.
The system is a little bulky, but the build is quite solid. Mine has taken a couple 1.5 ft. coffee table to floor drops thanks to my dog, and it's kept on ticking. I know they also make a slim line T440s and even an ultrabook (T440u) version although that might require giving up some features like the Macbook Pro.