In KDE 3.5.x we had kicker, but for KDE 4, it has been killed and replaced by the most famous part of the KDE technologies, known as Plasma.Plasma is, among other things, the new way of building your desktop, it works using Plasmoids, those Plasmoids are similar to Gadgets or Widgets.
Plasmoids are contained by... well... containments, this relantionship it's the secret of its flexibility. The Desktop (image background) is a containment, you can put as many plasmoids as you want, those can create a normal interface showing your /desktop files, or you can put clocks, stocks viewers, media controls, pictures, etc. However, the panel is a cointenment too, you can place your Plasmoids in your desktop or in the panel, Plasmoids will change their layout to match correctly their new containment.
The biggest point here, is that cointenments are Plasmoids too, so, in the future, people (or KDE developers themself) can (and certainly will) create new containments, of all kinds. Making a OS X dock or a Windows 7 like taskbar shouldn't be that hard.
New and Improved KDE Kick OFF Menu with stunning Plasma Theme
Note : The preview posted here is based on Pre-Beta1 Release of KDE 4.2 which will keep on maturing as time passes. Most of the KDE apps like K3B , Amarok and others will début with KDE 4.2 for KDE 4.. Few already launched KDE 4 apps are KDEnLive, digiKam Beta , Amarok Beta , Gwenview and lots of new and improved K Tools.
For More Detailed Preview Of KDE 4.1.72 [Pre Beta] : Introducing KDE 4
Check out my KDE 4.0.4 vs Gnome Test : http://www.techenclave.com/open-source/kde-4-the-lightest-desktop-yet-114725.html?highlight=Desktop