Vaughan-Nichols makes a good point in his article that we do have most of the basics with Linux on the desktop – a GUI desktop interface, basic office products, Firefox, and other applications. For many users, especially those that rely on their computer for email and web surfing, this is most or all of what they need.
There are still a few gaps. People tend to have one or two apps that they "just cannot possibly live without." Vaughan-Nichols used Intuit QuickBooks as his example. Right or wrong, the unavailability of these apps will keep certain people from migrating to Linux.
Another gap is vendor support. Too many hardware vendors don't release drivers for Linux in a timely manner. While this isn't a big deal for techies who can either write a driver or find and install one from the Internet, this would be a big deal for someone like my mom, who wouldn't know what to do if her printer didn't immediately work when connected (no plug-and-play).
For now, Linux on the desktop will probably be most popular with the techies, but as it continues to gain traction, more and more people will get on board.