TBH I don't think usability of either gnome 2 or kde 4 are currently really an issue for linux. Linux noobs are more likely to face problems with hardware drivers, finding suitable linux software and other issues involving the relative obscurity and multi distro and geeky nature of linux.
Gnome 3 and unity are not here to address some non existent problem with desktop usability. They seem to be about creating a gui that works seamlessly on both desktop and tablet. They both need work but I quite like gnome 3. Although that's the kind of 'like' where I would never use it myself in its current form.