Incremental releases for large projects are often grab bags of unrelated features. However, KDE SC 4.4 beta 1 (aka KDE 4.3.80) is a welcome exception to the rule.
True, the release includes new applications and improvements to existing applications on the KDE desktop. But it also features improvements to general desktop functionality and the evolution of several technologies and directions introduced earlier in the KDE 4 series of releases. In other words, it is ambitious, with far more innovations than than the average incremental release.
As I write, binary packages for KDE 4.4 are still finding their way into distributions. According to the release page, packages are available for Gentoo and openSUSE 11.0 and higher.
However, you can also upgrade to the upcoming Ubuntu Lucid Lynx release, and from Debian's Experimental repository. These sources provide a mostly complete preview of the new version of the KDE desktop, although in some cases you will find that new applications are not included.
For most users, the least interesting changes in KDE 4.4 are probably the changes to standard desktop applications. Some of these, like the use of Akonadi, IDE's personal information engine by Kaddressbook, are behind-the-scenes improvements that may go largely unnoticed by most users.
Others, like Bloglio, a basic blogging tool, or educational programs like Cantor and Rocs are new applications that you have to install specifically -- assuming, of course, that the distribution you are using have packaged them. Through no fault of the applications, all of these are easily overlooked, especially if you are only mildly curious about the beta.
In still other cases, the applications are already reasonably mature, so that many of the most noticeable changes are minor ones. For instance, if you use KRunner, the supercharged run command and menu substitute, you may be interested in the fact that it now works with bookmarks or opens by default anchored to the top of the desktop -- but, chances are, only mildly so.
For the average user, the most interesting new application is apt to be Plasma Netbook, the new KDE desktop for netbooks presented in the beta as a technology preview. When you start Plasma Netbook, it replaces the standard KDE desktop until you close it from the taskbar. If you are considering running KDE on a netbook or any other small screen, then you should find a look at Plasma Netbook well worth your time -- it's one of the most promising netbook desktops I have tried.
Since the radical redesign of the desktop in version 4.0, KDE has been spent the last two years gradually adding usability. Much of the groundwork in usability has been done in earlier releases, but 4.4 adds refinements to help fine-tune usability.
Since 4.0, KDE has had Activities, eventual replacements for Workspaces, but not emphasized them. In fact, they have been mostly hidden in the menu of the Desktop Toolkit ("the cashew" in the upper right corner) under the item Zoom Out.
Now, in 4.4, Activities are finally mentioned specifically in the menu, making users more likely to actually use them. Go to Multiple Desktops in System Settings, and you will also find an option to associate a different Activity with each desktop -- a much-needed step forward in removing the confusion between Activities and Workspaces.
Another welcome change is the additions to the hotspots on the edges of the desktop. In System Settings -> Desktop -> Screen Edges, you now have several additional options for compositing effects when you move the mouse over a hotspot.
Moreover, in a possible answer to Aero Snap in Windows 7, KDE 4.4 adds the option to maximize a window when you move it against the top of the screen, or to tile it vertically when you move it to the edge of the screen. Such features require that you stay alert to avoid activating them accidentally, but might help to reduce repetitive stress injuries from clicking.