Running what appears to be a touch UI (definition: very few buttons, those that exist are large, lots of dead space, information density very low) with a mouse feels shockingly unproductive, and at least personally, conveys the impression of working with a mobile app toy rather than a workstation used for getting work done.
GNOME3's launcher: http://i1-news.softpedia-static.com/images/news2/GNOME-3-16-...
You can't look at this and not see shades of iOS's Springboard. Very touch friendly on small mobile device screens, very wasteful on large ones, like the kind most of us have at our desks.
...and like the kind that most of G3's users will be running it on.
I'm forced to write off G3 as yet another misguided attempt to unify touch and mouse UIs, in an attempt to appeal to the kind of newbie user that wouldn't even be running G3 in the first place.