How great is "great"?
My new employer has given me a new Macbook Pro, and Kubuntu mostly works, but it will require some manual fiddling.
Booting, thunderbolt ethernet, thunderbolt display, wifi, external mouse/keyboard, external HDD, and all essential things do work. Disconnecting and reconnecting the display works 90% of the time, which I'm pleased with -- KDE now remembers where my toolbars and windows should go.
I don't have power management working, the touchpad is half-working (no scrolling), and I gave up getting the retina display + an external standard display to work -- I've reduced the resolution of the retina display.
I haven't yet put much effort into fixing these things, partly because I don't know whether they can be fixed (in reasonable time) and partly because I'm busy with the new job.