The proposition "software X has comparatively bad usability" is expensive to provide additional evidence for. The existing evidence includes the typical experience of people new to FOSS using things like Emacs, VIM, Gnome or GIMP, a difficult-to-explain preference for proprietary software among professionals in various fields and among typical consumers, each person's individual experience, various critical analyses of free software by usability experts studying the problem, and sundry other evidence. If this isn't enough to convince you that free software broadly has comparatively poor usability, the odds of discovering additional evidence that would convince you is probably too slim to be worth the effort. But it's a premise many of us accept. For those among us who do, blog posts like this provide some insight.