This will never happen. We all waited so many times for Dell to make Linux first class and it never happens. Painfully the truth was always clear - there was no reason because Linux desktop would never approach anything remotely close to Windows in terms of usability and demand.
However, every web app that I've deployed (dozens) always had/has Linux on the server. For me, I nor the teams I worked with would consider anything else.
However, for the desktop, I gave up on that in '02. Went to Mac, never looked back. Linux server succeeds because it doesn't require any UI pleasantries. Desktop is a completely different story because it does. As much as I support the FOSS movement, I just don't think it has what it takes to make a compelling desktop. Ubuntu and others can copy OS X, but I don't think they'll ever make a comparable, competitive alternative.
What most people probably don't realize is that Apple is a laptop company. No one in the industry can match their industrial design. If you set down in front of anyone (who cares about their tools) Brand X laptop or a Mac laptop - it's no comparison. For me, software is my livelihood and I care about my tools and plastic junk is plastic junk.
This stretches out even further though because all those hardware decisions inform the OS decisions. It's not like, "yah, just use this ethernet chip" or "whatever, just get decent battery life, use whatever cells you need". Everything is considered. Every millimeter, every curve, every line. If a custom battery design is needed, then it is and it's made specifically for that device. If they don't have enough room for a typical laptop cpu, they go to Intel and ask them to make them one. No one else in the industry does this.
Ultimately I think these are the critical things. Design 100% matters. I recently work at one of the most prominent design companies in the world and I saw it all around me every day - they designed things for a reason and when you used the prototypes you were like, man, that totally makes sense. As a software developer, I'll never forget that - it reinforced my appreciation for things well thought out and it made it easy for me to deliver beautiful and well enjoyed products.
Lenovo, Dell, HP, etc - those companies produce things that are just 'made'. No one at any of those companies says 'make me a machine that looks like a flower' or 'how can we do something completely different?'. Their bottom line is the bottom line, so the cheapest materials go into every machine 'made'. This philosophy permeates the entire organization. So how can the 'greatest' desktop be 'made' for machines like this? It can't.
For servers where design doesn't matter as much, Linux is 'it'. It's fast, stable, gets out of my way and runs all the components I need. On the desktop, though, it's hobbled by hardware people that just don't care. Linux desktop needs someone to care in order for it to be a contender for the hearts and minds of ordinary users. Less is more in this case and a small group of people that can make design decisions for the future is what's needed to make Linux desktop something people would want to use. Something better than Windows.
But, to catch up to OS X? I don't think so. Especially now since it's being influenced by iOS.