That wretched Unity disaster is why I never moved my kids' desktops on from Ubuntu 10.04 until the last few days when I installed Mint 15 XFCE on them.
XFCE is a little different to KDE or anything Gnome based (I don't like what Gnome has become either) but it's also much lighter on system resources than either. There's lighter still of course, but the leaner you go the less friendly they got.