I'm giving KDE another try - so far so good. I installed everything using
apt-get install kubuntu-desktop. During the installation it asked me which login manager to use and I chose LightDM - however, now I'm finding user sessions (KDE) are behaving a little funny - when left for some time, they lock out asking for password, but there's no way to switch user (i.e. there's a small window asking for password with Ok and Cancel buttons - no Switch User, Shutdown, Suspend or anything).
Pressing Ctrl-Alt-F[something] shows a text log, where I can see a message "Not starting KDM because it's not the default manager" - so I think my problem can be fixed by making it default.
How can I do this?
(actually, trying to switch user via K-menu - Leave - Switch user results in the same dialog: "The session was locked by sergey, please enter your password")