I think one reason Linux user interfaces have been catching up with Windows (if not Mac) is that for the past ten years or so, desktop-app usability has remained stagnant (or, in the case of MS Office, regressed).
Twenty years ago, Apple and Microsoft had to convince non-geek consumers that personal computers were worth buying, and so they had an incentive to make their products as usable as possible (given the constraints of cost and technology). Now that consumers see personal computers as things that they have to use whether they like it or not, there's not as much incentive to use the UI. Instead, people shell out their own money (or, if they're lucky, their employers' money) to take "how to use Microsoft Office" classes.
"Linux user interfaces have been catching up with Windows (if not Mac)" is a common misconception.
I love the tabbed file system views in Gnome. It's much more comfortable than the Finder. Windows Explorer too is simply terrible. I have been using Windows at work and Gnome at home and can't even begin to decribe all the ways Windows is completely broken from a usability standpoint. People tolerate it because they know nothing different and/or are unwilling to learn.
In many aspects, Gnome and KDE have already surpassed Windows and OSX.
Twenty years ago, Apple and Microsoft had to convince non-geek consumers that personal computers were worth buying, and so they had an incentive to make their products as usable as possible (given the constraints of cost and technology). Now that consumers see personal computers as things that they have to use whether they like it or not, there's not as much incentive to use the UI. Instead, people shell out their own money (or, if they're lucky, their employers' money) to take "how to use Microsoft Office" classes.