I successfully updated both our computers. Mine already had LMDE UP3 that I recent installed KDE 4.6.5. The upgrade went fairly smoothly, but crashed once in the middle. I restarted MintUpdate and it went completely through the second time. Everything is running just beautifully. It appeared to install Gnome 3.2 as well as KDE 4.7.4. I suppose I had some Gnome dependencies that required it. I saw Gnome 3.2 show up in the list as it was installing, but I can't really see any evidence of Gnome Shell anywhere - as I shouldn't.
Oddly enough, LMDE Xfce on my wife's laptop upgraded UP4 the same way. It crashed the first upgrade try and succeeded the second one. I'm not sure there there is some weirdness in the install of UP4 that cause both of these, but thought I would report it anyway.