This thread shall be a compilation of materials on usability. Can be Tor related usability (research) and also general usability.
On usability, I recommend watching the following video. Worth the hour.
I have a strong conviction that there is a huge disconnect between technical people and laymen. More so of programmers and laymen. Specifically in the Free/Libre Software community. Small teams without having knowledge on usability, let alone the ability to do usability research, let alone a usability designer or at least a usability advisor are producing software which most laymen fail to use. We have evidence for that as in usability research and can extrapolate from there.
Usability can be neither implemented by chance nor is intuition a guide to how laymen will be capable of using the software.