It is...until it isn't. Nine out of ten Ubuntu or Mint installs will go off without a hitch, with no weird issues or regressions, and a warm, friendly, comfortable development environment welcomes you. Then there's that one time you install it on your laptop so you have a to-go environment that matches your workstation, and BOOM! your wifi isn't recognized (what year is it again??) or your sound card sputters (damn you PulseAudio!), or your hybrid graphics screws the pooch. Hell, I built this workstation I'm typing on with GNU/Linux and BSD compatibility first in my mind, and I still had issues with some hardware right off the bat. Nothing that can't be fixed with some fiddling, but it's annoying as hell.
Yes, all of the above issues can be fixed, just like the issues you dealt with in OS X. It's a computer, after all; Garbage In (Apple/Linux/BSD developers), Garbage Out. And don't get me started on Windows 8.x; it's finally becoming usable daily, but there are a million reasons I chose to stick with 7 for Windows-specific work, and wait it out until 10 ships.
Apple broke the cardinal rule: If it isn't broken, stop fixing it! They want to innovate and improve and conquer the world, fine; but they need to remember that they had the best OS X release with Snow Leopard (and in my personal opinion, that was the best desktop OS period). In their rush to wow the masses, they broke their OS for those of us who use it to be productive and creative.
At this stage, I feel that a good old fashioned, stable OS like FreeBSD or Slackware Linux or Debian is the best choice for a solid 'nix workstation, something you can get real work done on. But ever since Lion was released, I would rather use Windows Vista on a Core Solo machine than OS X on any Mac.