I even backported the then-current version to MacOS X 10.4 (Tiger) last year. :-)
Bluetooth is very broken too. Not sure if that's an issue with the drivers or the Linux bluetooth stack in general. Fortunately I only use it for my wireless headphones, which I can live without.
WiFi used to be a big problem when I tried Linux on a Mac at a previous job, thanks to terrible Broadcom drivers, but that all seems fine now.
Been running Linux on a Mac for 2 and a half months now, for me personally the improvements are significant and the issues minor.
When the software doesn't handle it well. I don't particularly like any implementation of high DPI scaling. OS X's scaling caused performance issues for me, and programs would get confused moving between monitors. Linux doesn't have any way that I know of to cope with monitors with significantly different resolutions - eg, I can make the window manager scale everything 2x so it looks good on the 'retina' display, but I still have a 1080p monitor attached too, so then everything is huge on that.
Even without multi monitor issues, scaling tends to be picky with some programs on most OSs. OS X seems to be the most consistent, Linux is a roulette wheel depending on your GPU/window manager/program/day of the week. Windows works sometimes but looks blurry.
I have Linux installed on my work Mac and just run the 'retina' screen at 1920x1200.