The KDE people ask me to post the bug here b/c it seems to be Gentoo specific. In short: kdeprint preview doesn't work if the _internal_ viewer should be used (kpdf and gs are already installed). The full story is here http://bugs.kde.org/show_bug.cgi?id=137425 This I found which could be related to this bug: tfoerste@n22 /usr/kde/3.5/share $ grep -Hir kuick * ... applnk/.hidden/kuickplugin.desktop:Name[de]=Kuick - Kopieren und Verschieben ...
Tracking this bug upstream.