I've used OS X at work for the past 2 years and I completely disagree that OS X is nice for developers. I've had a lot of issues that I wouldn't have had if I was using a GNU/Linux distro like Debian. Major issues with GCC after certain updates, outdated GNU software like bash, brew is barely acceptable as a package manager (can't hold a candle to dpkg/apt), and I have to go to websites to get the installers for most…
As for the UI, until Mavericks I think it was behind the last stable Gnome 2 release. Now it is ahead in some areas but still behind in others.
Finally, Ubuntu continually screwing up things like audio support or ruining areas of the UI (ironically to make them more like OS X) also helped me make the switch.