Linux has somewhere between 15-24% of the world market (depends who you talk to) thats a pretty good foothold. If you want to talk plainly about why it wont penetrate the desktop more you need to look at 15 years of code written by companies to run on one operating system. Heck I could get linux desktops deployed with little to no resistance from upper management and users if only we did not have so much dang powerbuilder code floating around..
I think the future is now, with OSS and closed source in the same echosystem. Sun uses Samba, SCO uses webmin, VMWare uses a linux kernel for the console, and all these companies save money to focus on their business focus...
Is that server or desktop? I can believe it has almost 25% of the server market, but no where near that amount for desktops.
For Linux to heavily break into the total marketshare it needs to get more agressive in the desktop arena, not just server. I agree with your statement "I think the future is now, with OSS and closed source in the same echosystem". In just the last year that we've been on this thread I've seen Linux make some impressive moves and gains. The future for Linux is wide open and limitless