Maybe it's just me, but I simply can't understand why people get so fussed about "the desktop"! Isn't it just a place to park files and start apps from?
My job involves Linux and Windows systems. On my desk is a monitor connected through a KVM to a Linux desktop and a Windows desktop, which I use fairly much interchangeably.
What I look for are apps that work as near as possible identically in both environments. My top five are Firefox (check), Thunderbird (check), NX Client(check), Gnome term or PuTTY session running ssh (check), OpenOffice (check). I think they'd also be the same on a Mac, if I ever have cause to use one.
The real Windows problem is application lock-in. I can't run Exchange on a Linux system, and Microsoft Exchange Server IMAP support sucks - almost certainly by design. OpenOffice can't yet correctly open every MS-Office created document, and were it not for the EU court, OO.org would have been placed at an ever-increasing disadvantage by Microsoft. Windows contains an unknown number of undocumented WINE-trap system services - ones that are there solely to hurt people running MS apps on Linux systems. Most desktop software vendors don't sell Linux versions, and many further trap you with undocumented proprietary file formats. Turkeys DO vote for Christmas, if you get your propaganda right.
This is why Windows will not be going away in a hurry. Not any deficiency of Gnome or KDE compared to Windows desktop. Not the (diminishing) number of hardware vendors who refuse to co-operate in the development of Linux drivers (perhaps there are now enough companies putting such hardware on a no-buy list? We go for Intel or ATI/AMD wherever possible).
A friend is running a small business with Linux systems only - no Windows unless there is a business-critical requirement for it with no alternative. So far, small-business accounting is the only exception, he'd love to get rid of the only Windows system but there is no sensible tax authority approved small business accounting system that runs on Linux. (Thanks, government, for forcing us to spend our money with a foreign multiply-convicted monopolist!) But there's no problem with staff learning to use Gnome and Openoffice on the job, they might prefer Windows/Office for the first few hours, but that's not what they are being paid to use and they rapidly adapt. It can be done.