There are still many users of other operating systems who think that Linux is behind Mac OS X and Windows in terms of desktop design, but the reality is just the other way around.
Linux doesn't have any kind of PR, and in the collective mind of the people, there is still an impression that Linux users spend their time inside the terminal and in dreary desktops. In fact, most of the current Linux desktops are much better than anything made by Apple of Microsoft.
When a new operating system is launched from Microsoft or Apple, it stays pretty much the same as long as it's supported, and even when updates are released, the desktops change very little. On the other hand, Linux developers are pushing the boundaries of what can be done in an operating system every day, and new ideas and applications that enhance the desktop experience are popping up all the time, regardless of the OS devs are doing on their front.
The spirit of the collaboration in the open source ecosystem, and the fact that Linux users are completely free to modify their system in any way they want will produce desktops like the ones in gallery below.
Both the Mac OS X and Windows users are trapped in the design jails that basically lets them take two screenshots that remain the same for years.