Dec 13, 2005: "I encourage people to switch to KDE. This 'users are idiots, and are confused by functionality' mentality of Gnome is a disease." - http://mail.gnome.org/archives/usability/2005-December/msg00...
Jan 26, 2009: "I thought KDE 4.0 was such a disaster I switched to GNOME. I hate the fact that my right button doesn't do what I want it to do... the whole 'break everything' model is painful for users and they can choose to use something else." - http://www.networkworld.com/news/2009/012209-open-source-ide...
Jul 26, 2011: "I used to be upset when gnome developers decided it was "too complicated" for the user to remap some mouse buttons. In gnome3, the developers have apparently decided that it's "too complicated" to actually do real work on your desktop, and have decided to make it really annoying to do.
I'm using Xfce. I think it's a step down from gnome2, but it's a huge step up from gnome3. Really."
Linus has always endorsed being pissed off at your interface and ditching it for something radically different. The current move, as you can read, is not one of satisfaction with XFCE. Clearly Linus just thinks all UIs are shit, and maybe that's a signal no one has figured this out yet, or maybe it's just a signal he's a curmudgeon.
(Edited for typos - I kept swapping 'Linux' and 'Linus.')