LightDM will probably replace KDM in Kubuntu 12.04 and David Edmundson has started working on Qt bindings and a KDE front end for LightDM. The greeter (theme) allows the use of Plasma widgets, can be configured independently and is still very fast, says David.
This is work in progress, but if you're using Kubuntu 11.10, you can already try the KDE LightDM greeter by using the ppa:agateau/lightdm-kde PPA in Kubuntu 11.10 Oneiric Ocelot. In David's screenshot (in the beginning of the post), you can see two themes as well as a LightDM configuration dialog available in the KDE System Settings - for now the System Settings integration and the second theme aren't available in the PPA, but if you want to give them a try, get the latest code via GIT.
To test (this is not stable!) the LightDM KDE Greeter in Kubuntu 11.10, use the commands below:
sudo add-apt-repository ppa:agateau/lightdm-kde sudo apt-get update sudo apt-get install lightdm-kde-greeter sudo ln -s /usr/share/xgreeters/lightdm-kde-greeter.desktop /usr/share/xgreeters/default.desktop
Arch Linux users can install it via AUR.
When installing the LightDM Greeter package in Kubuntu, LightDM itself should install too, and you should see a message asking you to select if you want to use LightDM or KDM as default. Select LightDM and restart your computer.
If somehow the message doesn't show up, you can switch to LightDM using the command below:
sudo dpkg-reconfigure lightdm
If later on you want to use KDM by default again, run:
sudo dpkg-reconfigure kdm
And select KDM as the default display manager.
More about switching between LightDM, KDM, GDM, etc. in Ubuntu.
via / first screenshot credits: sharpley.org.uk