Kubuntu 12.10 has been the first release to ship with LightDM which has replaced KDM as the default login manager. This follows the same step made by Ubuntu in previous versions which seems to have been quite successful.
About The Change
We can all thank David Edmundson who has been the primary contributor to LightDM-KDE which has already reached version 0.3.0. LightDM is a better prospect for the future of Kubuntu for many reasons.