We're a Linux shop with around 400 desktops and have been running KDE for a decade. KDE3 was rock solid. KDE4, not so much. The KDE4 direction of "let's index everything" with nepomuk and akonadi doesn't work so well when home directories are NFS mounted. In fact, it killed our fileserver. Further, why on earth would I want 400 instances of mysql_community_server running and creating a 128MB DB for each user in their home directory just to index their PIM?
In general KDE login times have been getting longer and longer, and the overall flakiness of KDE up to 4.6 have led us to dump KDE in favor of XFCE. Initial feedback from users has been very positive, and we'll be completing the transition this summer.
KDE4 may have some features that are fine for a standalone desktop at home, but it took a giant step backward from KDE3 in terms of usability in a networked environment at work.