Becoming a KDE Tester
In the early 2000's there was a specific team at KDE which was focused on finding loose ends in KDE applications and tying them together. This was a task of user case studies, writing articles, documentation, creating missing artwork for consistency, and other miscellanea. Ultimately, this team contributed patches of code and documentation that really rounded out the KDE experience.
Communicating with the team
There is no active KDE quality team, but if you are interested in contributing improvements to KDE, you will be well received at #kde-devel on irc.freenode.net.
User interface is a very wide subject, and very subjective too, as something obvious to someone is absurd to others and vice versa. Therefore, don't assume, argue clearly, stating your logical steps. Your main tool discussing it are objective reasoning and good sense.
It is easy to perform a quick user interface analysis, but it is hard to convince people to change the interface. A good, convincing analysis can gain much if it incorporates information from the KDE guidelines, competing program and operational system analysis, general design principles found in many books, user testing or individual (anecdotal) feedback. It is a volunteer project, and even if everybody agree with you, someone has to implement it.
The KDE Usability Mailing List is very active and a good place for discussing your ideas, and their homepage is at http://techbase.kde.org/Projects/Usability. If you are already an usability expert, please check OpenUsability.org, a project that brings open source developers and usability experts together, and is collaborating closely with KDE.
Some projects for analysis of user interfaces may include: checking that shortcut keys are coherent across KDE applications, making sure that dialogs are directly relevant to the interaction that the user would expect, and finding users of KDE software to see how they perform common workflows.