Years ago Linux desktop usage was a bit of a drag. But at the time, Windows servers were so much worse that as an integrated system, you were still net ahead.
Now that my printers, scanners, and peripherals have all worked without hassle for years there isn't even a trade off. Rather, I shake my head while watching people fight with driver wizard CDs.
Now, I regularly tear my hair out trying to interact with Linux users. From diagram software (OmniGraffle/Visio) to accounting software (QuickBooks) to billing software (Billings by Marketcircle), Linux just doesn't have the solid, polished applications, and it interoperates exceptionally poorly in environments where Mac OS X and Windows get along just fine.
For example -- I can easily share diagrams with Visio users, but Dia is not a replacement for Visio/OmniGraffle and won't do the trick. How am I supposed to diagram with Linux users? Use dot/graphviz and create remarkably ugly diagrams?
If I had to assign blame for the lack of quality applications, I'd say that the APIs are unstable and inconsistent, there's no standard application API (gnome vs. kde/qt vs. straight qt vs. wxwidgets), the user market just doesn't exist, and that it's difficult to mix the GPL / free software world with expensive development that requires professional UI, design, and art work, and all the other components of a polished end-user product. End-users don't buy 'support'.
Of course, this is an unpopular opinion among free software advocates. As soon as you figure out how we can share diagrams that I want to place in my LaTeX documents, interact with artists producing photoshop/illustrator files, and modify complex word documents sent by lawyers without losing required document meta-data -- let me know.
What is "professional UI"? How is a UI Professional? What qualities make a UI Professional? That's a pretty ambiguous qualifier.
I'm floored.
It seems to require a paycheck to convince anyone to produce feature complete business accounting software, and even then the A-list individuals are probably otherwise occupied with more enjoyable projects.
In the phone market, such a large, self-perpetuating commodity hardware platform has yet to evolve. The market is heavily balkanized. It's under the control of multiple carriers whose rules determine exactly what will be sold and where. It's a rather different universe from that in which Linux evolved.