While the Gnome desktop is the de-facto for Ubuntu, try the KDE alternative if you want the best-looking and comtemporary Linux UI, says APC's Linux guru, Ashton Mills.
KDE is an interesting beast: up to version 3.0 it competed with Gnome for the mind share of Linux desktop users. KDE 3.0 was an excellent alternative, often favoured by the power users for its emphasis on configurability and flexibility.
For version 4.0, the KDE team took the drastic action of re-inventing and re-building KDE almost from the ground up. This included re-designing the desktop paradigm and breaking functionality into core components that include Plasma (desktop display and effects), Phonon (multimedia backend) and Solid (hardware abstraction layer).
For its initial release KDE 4.0 was buggy, lacked essential features, and most KDE applications weren't ready for it. In many ways, this set KDE back for during this time Gnome continued to improve on its solid and established base. And I'll be the first the say that Gnome is reliable and works well as the first experience of Linux that most often accompanies users making a transition to Ubuntu.
But now at version 4.4, and with 4.5 on the way, I'll also be the first to say that KDE is rapidly leaving Gnome in the dust. The gamble to re-work and re-design KDE at the height of its popularity is starting to pay off. Indeed while my current main desktop is Ubuntu 10.04, I'm now thinking that come the 10.10 release it might be Kubuntu greeting me in the morning.
What so different?
One of the reasons that KDE is starting to stand out is its underlying rendering architecture. While Gnome can look quite snazzy with 3D-accelerated effects thanks to Compiz, in many ways its like putting lipstick on a penguin. Gnome still sports, after all these years, the same underlying GTK backend which harkens back to Windows 95 days. Compared to Windows 7 there's no Linux alternative to clean, fast, integrated desktop effects that ply their way through the environment from top to bottom. Except for KDE. The closest thing Linux has to the Windows 7 desktop in terms of functionality and eye candy lies firmly with KDE 4.0. You only need to browse the screenshots to get an idea.
But of course, a desktop environment is much more than how it looks. When it comes to day to day use, how does KDE compare to Gnome, and is it something you want to use?
The anti-desktop
KDE's default view separates your desktop from the underlying filesystem and calls this an 'Activity'. You
can elect it to display your Home folder, or any folder, as with Gnome but by default objects on your desktop fall into one of three categories: widgets, folders, and icons. In truth, the folders and icons are widgets too - in fact, the very paradigm of the KDE desktop is that (almost)
everything is a configurable, moveable widget: the task bar, the clock, folder views, documents and so on. Click on the clock and a calendar pops up, drag the pop-up into the desktop and it detaches as a separate widget. Interestingly, widgets can also be shared across a network - a system monitoring widget can be loaded across the network to see the statistics of a remote computer.
KDE allows for stunning desktops While filesystem management is managed by Dolphin (think Nautilus but - as is the way with KDE - with considerably more settings to play with), you can still move files and folders around on your desktop too - just that they represent links, not the objects themselves. And to organise these you have Folder Views. Think taking your current Gnome desktop and all the files and folders you use on it, and putting them onto the KDE desktop in a view called 'Desktop Folder'. Everything else on your desktop is there to help you work - or play - through the use of widgets.
Transparency effects are clean
and fast. And as discrete graphical objects, all of them have at least some common functionality between them: to be configured, rotated, resized, launch parent applications and of course remove them.
The only confusing thing is that not only can you have multiple 'desktops' as with Gnome, you can have multiple 'Activities', each of which can have multiple desktops. It's easy to get lost if you're not careful.
Functionality
The expected functionality of desktop integration, including the messenger (aka Ubuntu popping up messages in the top right) is all there, but with KDE's own twist. Plug in an USB key for example and popup will display all currently plugged in devices. Hovering the mouse over a USB device will show how much space is free, while underneath a message states how many actions can be taken. If you click, a drop down a box shows for example 'Download photos' or 'Open file manager'.
In terms of interface all the expected paradigms are there -- the task bar, notification area, applets (widgets) and menus. One key difference is that where Gnome breaks the top level menus into Applications, Places and System KDE bundled this all under the K Menu with 'Places' being found as 'Computer' on the K Menu, and System utilities being bundled under a System menu. While it does look better, I personally don't mind the breakdown under Gnome, as it can save a few mouse clicks.
Many of the default apps, with the exception of graphics where The Gimp dominates, are arguably better on KDE as well: Amarok is the best music player/manager on Linux by far, K3B is a brilliant CD/DVD mastering application, Ktorrent is an excellent torrent client (which I used for many years on Gnome before finding Deluge), Kopete a fully featured IM program, and even Dragon Player as the basic media player is a better tool than Totem under Gnome.
The Run toolbar doubles as total
system search and launcher. For browsing Konqueror is the default browser, based around KDE's own KHTML. It's worth noting KHTML was later forked into Webkit and adopted by Apple for Safari, and then by Google for Chrome. So it has a very sound grounding. That said, Konqueror itself was initially designed as a web browser and file manager and, as such, isn't as feature rich as browsers like Firefox. Which highlights the fact that, if you want to, you can run Gnome programs on KDE just fine (and vise-versa). KDE actually dedicates one of the subsections under Appearance to how Gnome apps look under KDE.
While KDE is beautiful, I will say the default button theme is kind of bland, but this is easily replaced. In fact, most of the themeing elements are easier to play with than Gnome too: for backgrounds, buttons, icons and more there is a 'Get new...' button that pulls in collections from the net and displays them with previews. Adding them is as simple as clicking on Install. This ease of getting new content applies to widgets too -- you don't have to go hunting for them online and figure out how to install them, KDE does this for you. And there are
lots to choose from.
Is it all good?
If there's a common criticism levied against KDE it's that it's the opposite to Gnome in terms of hiding, or enabling, functionality for the user. Gnome is at times a little bare for options, while KDE is sometimes overwhelming: flooding simple menus with dozens of options you may not use. Everyone's different, but I'd personally like a balance between the two. Perhaps that can be partly solved by distributions - it's worth noting Kubuntu isn't the only KDE-based distribution, there are many others, including the most popular distribution in Europe: SuSE.
Perhaps the biggest hurdle to KDE for Gnome users looking for a change is simply learning something new: the desktop paradigm, the different menus, and the different default applications (though you can continue to use Gnome apps too). But on the whole if you haven't considered KDE before, I do recommend giving it a go. Now that it's stabilised and into the polishing phase, it's pretty clear that Gnome will eventually be made obsolete -- at least in its current incarnation. Microsoft made the visual jump from XP to Vista and now Windows 7. KDE made the same jump from KDE 3.0 to KDE 4.0. But Gnome is living on borrowed time, unless it too undergoes a metamorphosis. Which it may just be doing.
MORE SCREENSHOTS
The KDE login screen. 
ABOUT THE AUTHOR
Ashton Mills has been using Linux since Slackware came on floppies - and before that, was one of the three people in the world who used OS/2 (and loved it). Always ready to make the most of his PC, he is constantly playing with Linux distributions and compiling the latest kernel.