KDE, while extremely customizable, always lacked a tool which resembles the eye candy Ubuntu Software Center. One may argue that USC is not as powerful as plain Synaptic Package manager, yet it is polished enough to attract average user. KDE's own Apper comes close but there are some missing features which keep it below the USC.
The good news for KDE fans is that the developers are now working on an improved Apper. Credit goes to the GSoC work done by Ximion who created the AppStream framework.
The developer has created a backend – AppStream core, which can be used by other package manager to provide better functionality to the software stores. Apper+ AppStream now looks like this:
As you can see Apper is now showing the applications instead of packages. The code is also cross-DE and can be used with PackageKit and in other distros too (not just Kubuntu).
Though its not yet stable, if you feel adventurous, you can grab the code from GIT.