What a daft question. Yet I've heard it repeated so many times that I almost get tempted to answer it.
Who's desktop, that is my counter question. Of course it utterly depends on what you want to use your desktop for, and more than that, HOW you want to employ your desktop. For some people no computer will be able to replace what they do on a drafting board, with an air brush, by means of filters and lenses, or using their lathe or whatever else. Those are probably the real artists.
The rest of us content ourselves with playing at it using whatever software we can find that best meets our needs. I loudly proclaim that don't have a single MS Windows file anywhere on my computers, but I secretly reserve the right to open a remote desktop onto my wife's PC from time to time and there run my favorite home floor planning program. (I have yet to find a floor planning/home design program which runs on anything other than MS Windows). By which I mean that each operating system has got some gaps and some areas where it excels.
I run Nevada on my work laptop, because it is the only operating system that is ready for the desktop. Qualifier: When at a customer's site I often need to be able to run core dumps, crash dumps, and explorers though analysis tools, jumpstart servers, and perform a few other miscellaneous tasks which are much harder to do on any other operating system.
On the other hand Linux is the only operating system that I can qualify as desktop ready when it comes to my normal desktop PC. On this particular system I try out new programs, fiddle with kernel options, play with hardware bits, do some (amateurish) video and photo editing, etc. I'm sure I could do most of that on [Open]Solaris or even Windows, but I'm not that masochistic. Linux just makes it easy for the enthusiast to get under the bonnet of the OS and scratch around. After a discussion with a colleague a few days ago I must say that this is not always a benefit (Linux by its very nature makes it difficult to support in a mission critical environment)
But the point I am trying to make is that you need to decide what you want to do, and how you want to go about doing it. Then next you need to consider whether there are any trade offs. Can you live with your Linux system not supporting your webcam, can you live with the limited selection of software applications available under Solaris, or can you accept Windows' inherent security and stability issues.
So next time you're tempted to ask whether your operating system is "ready for the desktop", please do qualify the question with what you use your "desktop" for.