It is a hard requirement I suggest to my friends. May be they run Ubuntu/Fedora, but if it runs well with Debian or linux-libre, rest assured, it should work with any Distribution.
I haven't yet seen much Laptops of notebooks to recommend though. https://h-node.org/ seems to be the only good reference.
More recently I had a regression for a few months, until the issue was identified (and fixed).
Both experiences made me more sensitive to Linux stability issues. If you look for it, you will find many bug reports. They typically are rather frustrating: they happen for some unlucky guy, but are hard or impossible to reproduce in slightly different contexts. I guess this can't really be avoided: both Linux and a modern PC are complex systems, and there are many variants. And no ODM doing integration tests (or not with your preferred distro of PC configuration). So some glitches are bound to happen. Considering the lack of ODM support and standardization, the situation is actually quite good. But there are bound to be glitches here and there. For those who want to avoid it, it's possible to avoid all this by getting a PC with Linux pre-installed, or with some integration test done (it seems to me there's some work done by Canonical for Ubuntu on some Thinkpad models, but not sure...). Also, not jumping on brand new laptop models can help too.
As for me, I prefer to stick with Debian on my laptop of choice, and handle the rare odd glitch when it happens. It's ok. Still, when I'll buy my next laptop I'll wait for the new generation to arrive, and buy the previous one. Cheaper, more stable with Linux, and not much hardware differences anyway nowadays.
I've not had any issues with my XPS 13 on it.
Meh. I'm writing this from an Asus EeePC which was once officially supported by Ubuntu, but now with broken graphics and wifi.
The non-free graphics driver is not included in Ubuntu anymore and the wifi works only with non-free binary blob.
Also, I recently found that wifi doesn't support channel 13 and 14 (found it accidentally when my laptop wasn't seeing the nearby hotspot) with the non-free blob. Now I run Debian testing.
Don't trust in those "Officially supported" things, unless it's Debian GNU/Linux. Otherwise, it's eventually going to be broken.
The channel visibility is regulatory thing; if you see only channels 1-12 you have set it for North America, most of the world can use 1-13, and Japan also 14 (for 802.11b only).
The world has changed from the times of the EeePC.
VPN reconnects ?
USB's and Card readers stay mounted ?
Audio mixer volume stays the same ?
Youtube videos and music player resumes ?
uptime shows the correct information ?
All of this out of the box in 2015 ? That must have been the year of linux on the desktop.