I have always preferred Kubuntu to Ubuntu for desktop installs, and that's one big reason. (Also, I've always preferred Konqueror as a file browser to whatever Ubuntu uses by default with Gnome.)

However, it's been a while since I've used it (I have 10.4 and XP machines for the most part), and I get the feeling that Gnome has benefited from Ubuntu far more than KDE has from Kubuntu, being sort of a bastard stepchild at best.

KDE's Konqueror has features that I still find myself wishing for on my Mac on a daily basis. (E.g., the visual view-by-size thing and built-in sshfs are my top two.)

I've not seen any compelling reason to upgrade my Macs from 10.4, so when they finally hit EOL I may seriously reevaluate Kubuntu as my main desktop, see if it's kept up reasonably well versus the mainline Gnome version.