You don't need to buy an old ThinkPad; current-generation ThinkPads work fine, as long as you avoid nVidia GPUs. All the other hardware (including power management) Just Works.
Well, a year or two ago, at least T440s ThinkPads came by default with a Realtek wifi card, for which there were no good Linux drivers [1]. Lenovo had an option for intel wifi card at no extra cost, but you had to be clever enough to choose that option when ordering the laptop.
[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1239578
There are various issues such as the laptop freezing when plugging in an external monitor (this can be fixed through a kernel update), crashes when waking from suspend / lock, Trackpad issues, problems with Bluetooth, problems with supporting 4k monitors through MiniDP, ...
So I'd say the stability of Linux on the new Skylake Thinkpads is far from optimal, although most of the hardware seems to be supported and runs.
https://www.reddit.com/r/Surface/comments/4nu355/finally_fix...
When my workplace gives a developer a new desktop (one of Dell's Ubuntu offerings, seems to always use AMD GPUs), that person's first day is normally setting up dual head.
I wanted to buy a laptop with a GPU for CUDA experiments.
I was looking at Lenovo Yoga 710 (14 inch with nvidia gpu). Am I going to have a bad time dual booting a linux distribution?
It's a mess.
Someone else in the thread said what I completely agree with if possible just get the latest Intel HD series it works pretty much flawlessly.
In modern laptops, you usually have the complication of 'optimus' which allows you to switch between the onboard Intel graphics and the Nvidia GPU. This can be a bit awkward to get working, but it's improved recently. I've had plenty of issues getting it working right on Windows too.
All three work great in Windows of course. For Linux, integrated-only is best, followed by discrete-only, and I've never had success with optimus.
It's my understanding that newer Thinkpads don't have the BIOS option to switch and that this is much more of a PITA to get working.
You shouldn't have issues with Nvidia hardware though.
You also want to avoid AMD Radeon, which is even more problematic than nVidia. I think the best advice is "as long as you go for Intel graphics".
That's where System76 comes in for me.
The X260 will likely work as an exact replica, but I haven't updated to Skylake yet so it's hard to say (ISTR there being some GPU buginess with Skylake at first). Otherwise everything should work almost perfectly out of the box, in my experience, though you'll probably want to tweak your power settings. The X260 will have a far superior screen, which if you're coming from a Macbook or anything will probably be important.
One of these days I'll upgrade and take my X220 down to the local hackerspace and get Coreboot put on it probably...
I'm a huge fan of the X1 series, which has about the same weight as the X260 but a bigger and higher-resolution screen. The X260 has the advantage of a hot-swappable, externally chargeable battery, and a better docking station; if you don't need either of those, go with the X1 and its awesome screen.