The KDE LightDM greeter is now up to version 0.1.0, which is now usable enough to make it into the Ubuntu 12.04 repository.
The LightDM KDE 0.1.0 greeter features three QML-based themes, guest log-in support, a KDE system settings module, and "a few bugs (maybe) and design quirks (definitely!)."
There's some screenshots of this LightDM-based KDE greeter within this announcement blog post
This release comes after months of LightDM-KDE being tested
and after extensive work on KDE/Qt-bindings for LightDM
were worked on in months prior
. LightDM replaced GDM within the Ubuntu 11.10 release
and continues to serve its role with the forthcoming Ubuntu 12.04.