I've had the XPS 9560 since February. I mostly run Fedora (26), but have also run Solus and various versions of Ubuntu. I have a Windows 10 install which I use for Photoshop, Lightroom, and some mobile gaming.
Specifically, the version I have comes with a i7 7700HQ, 32GB RAM, 1TB SDD and 4K screen.
Hardware wise, the laptop is lovely, and the build quality of mine is good, although it hasn't been perfect as I'll get to later. The screen is honestly the best I've ever used, although I do sometimes notice ghosting due to slow response times, I understand in that regard it's comparable to the retina displays used in MBPs.
Performance wise, the hardware speaks for itself. It's a very powerful machine. I haven't experienced any of the lag or video issues that others are reporting. It'll happily play games and crunch whatever data you throw at it, without any thermal issues.
My model was a very early version, and came with which I can only describe as a mushy keyboard which often did not register key-presses. I contacted Dell support, who after a short over the phone test, agreed it was not satisfactory and arranged for an engineer to be at my house the next day to replace the keyboard. This fixed the issue, and the keyboard has been fine ever since. Compared to the new MBP keyboards, I much prefer the 9560 due to the extra travel.
I've also had the GPU fan replaced due to it developing a grinding noise. Again, after a short phone call, Dell agreed to send an engineer to replace the fan the next day. The issue has since re-appeared, and although it's not a critical issue, I'll be getting Dell to replace the fan again. This does seem like a somewhat common issue, although I can't find any recent reports which would hopefully suggest it has been fixed on the manufacturing side. On the topic of noise, my particular machine has no coil-whine.
The webcam position is frankly bad. It's not an issue for me personally, but I do tend to place the laptop somewhere higher if I'm doing a video call - I can't be trimming my noise hair for every call I do.
I did try macOS on the 9560, as a bit of fun more than anything else, and it seemed to be usable after some effort. However I generally dislike macOS, so I'm back to using Fedora 26 which runs perfectly. Some older apps have slight scaling issues with the 4k screen, however nothing has proven to be unusable (yet). I haven't had any issues running a clean version of Windows either.
Overall, I'm very happy with the 9560.