It soon became clear during testing that different people have different expectations for a desktop, which is why they used them differently. We're not usability experts and the only measure of gauging comfort level was our groan-ometer.
While there was something to like about all of the desktops, KDE 4.7 drew the lowest number of groans. A major factor in KDE's success is its familiar interface. We're pretty sure if we'd put Gnome 2.x in the mix no one would have had any complaints. But, to be fair, KDE scored pretty highly, even after discounting the familiarity factor.
We also focused on testing the usability of the two new Gnome-based environments. All participants agreed that both are as similar to each other as they are different from Gnome 2.x. The results in this case were influenced by factors such as the form-factor of the device it was being run on, and how the desktop was being used.
In general, Gnome Shell 3.2 shines brightest on touchscreen devices with its large icons and polished on-screen keyboard. However, Ubuntu's Unity outguns it on every other platform.
According to our tests, out of the box, Gnome Shell 3.2 is best suited to users who run only a couple of apps and don't want to tweak their system too much. Users who like to pimp up their installs can currently do so, but might be better waiting until Gnome finishes work on SweetTooth, its framework for easier installation of Shell extensions.
A surprising result was that several experienced users decided to switch to Gnome 3.2's fallback mode, which looks quite different from the new Shell and more like the older Gnome 2.x release. There were even suggestions that the fallback mode should be the default to ease users into the new paradigms.
This is in sharp contrast to Unity's fallback mode, Unity 2D. Its developers are working hard to ensure that it resembles the full-blown Unity interface even on low-spec devices. This would explain why after testing Unity 2D, no one went back to it.
When all's said and done, though, every one of our testers was floored by KDE 4.7 across all devices. Only the most basic users noticed that instant messaging and other online services weren't integrated. There was a lot of praise for Activities, which was described as the natural extension to virtual workspaces on the Linux desktop.
Ultimately, though, your choice of desktop environment depends on how you want to use it. Since most popular distributions now support all three, you should really try all of them to see what fits your workflow.
If our tests are any indication, though, KDE 4.7 is the desktop environment to beat, with Unity 11.10 a close second and Gnome Shell 3.2 bringing up the rear.