On my system it is really KDE-3.4.2 causing this problem I installed only KDM-3.4.1 (without dependencies). On a gentoo system one can easily install an other version. At a new login I got a userlist and user icons back! I could not change the user icons probably because of missing dependencies.
Same problem here KDE-3.4.2 on gentoo. With my old system upgraded from older KDE versions no problem. But with a fresh install of KDE-3.4.2 no user list and/or user icons. Played also with a new kdmrc: no result. Changed also the showlist settings for the login manager: stil no user list.