Part of our work at Endless OS is around the usability of the GNOME desktop, guided by user testing. We're looking for test subjects for a 1-hour session, who are tech-savvy experts—e.g designers/developers, animators/…—with exposure to various devices & platforms. Bonus points if you're based near someone in the team—e.g. London—so we can put a laptop in front of you. Ping me here or to wjt@endlessos.org if you're interested!
(If you have worked on the design and/or implementation of the GNOME desktop, you're probably too close to the problem space—sorry!)