One of the major additions is the Plasma Netbook interface, which has been in development for a while now. "Plasma Netbook shares many components with the Plasma Desktop, but is specifically designed to make good use of the small space, and to be more suitable also for touchscreen input," the KDE team writes, "The Plasma Netbook shell features a full-screen application launcher and search interface, and a Newspaper which offers many widgets to display content from the web and small utilities already known from Plasma Netbook's sibling."
A lot of work has also been done to integrate social networks and other online services into Plasma, making it easier to manage those via Plasma widgets; there's a widget for posting to various social networks, as well as a widget for following what your friends are doing.
KWin has also seen a number of feature additions, which mostly can be summed up as: copy the hell out of Windows 7: move to the top to maximise, move to the left or right to fill half the screen (for side-by-side viewing). And you know what? That's a good thing. Just as Apple's Exposé, Windows 7's Aero Snap is simply a very handy and sensible feature that ought to be copied simply to make my life as a user easier. Kudos to KDE for implementing these features - whether they come from somewhere else, or not.
There's more to it than that, though. KWin can now tab windows together, with the titlebars turning into tabs you can switch between. Support for scalable graphics in KWin themes has been added, and performance should be increased too - still somewhat of a sore spot in KDE4.
The file manager, Dolphin, has seen improvements too. Search is now integrated into Dolphin and makes use of Nepomuk's semantic framework to help users in finding and organising their stuff. There's also a new timeline view which displays recently used files chronologically.
Under the hood, we see Qt 4.6, which brings with it a new animation framework, support for multitouch, and support for the Symbian platform. The KAuth framework leverages PolicyKit so that developers can write applications that can easily elevate privileges if the need to so arises - for instance within System Settings. KDE SC 4.4 also starts leveraging Akonadi, which "acts as a transparant cache to email-, groupware-servers and other online resources".
The impatient can build KDE 4.4 from source, but of course, it will find its way to your distribution of choice soon enough.