Graphics, music, and some small forays into movie production (although the real work still happens on Windows and the processing on Linux). Business-business, that being, engineering, finance, healthcare, point of sale, etc, still are Windows or Linux only clubs. For very, very good reason.
Funny, here in the middle of Silicon Valley, I see a whole host of MacBooks. I guess we don't do any real work like engineering. At least in the software world, they can't be beat. Since the vast majority of people developing for Linux have dedicated build/test machines, all you need is a thin client for ssh access. Add in that the Mac can run your collection of bash/perl/python/whatever scripts locally if need be, and it's the ideal dev machine. All this and you don't have to spend pointless hours forcing Linux to work correctly with your laptop. Yes, it's possible to make a functioning Linux laptop, but it doesn't "just work" like a Mac. And guess what? My company (and many others) would gladly pay the extra money for the Mac because it pales in value compared to the wasted time of engineers.
PS - Thank you. I've turned to near hatred of Apple over pretty much everything they touch with iOS. Thanks for bringing back the good ole early 2000s era Mac bashing and letting me release my decades-cultivated Mac fanboy. Who knows, maybe for old time's sake I'll install an OS X point release and come post about how snappy it feels.