While usability and open source software has come leaps and bounds with newer developments (Joomla, Alfresco, ruby etc.) sporting squeaky clean UI's, the nature of the OS development pattern has often left usability experts out of the mix, and shiny nav bars don't translate to ease of use. FLOSS is an ongoing attempt to bridge this gap.
FLOSS Usability, initiated by the non-profit, Aspiration, and the think tank Blue Oxen, hosts events designed to "catalyze greater shared understanding and ongoing collaboration between the usability and open source communities." In a previous "sprint" event (the fourth of its kind was held in March) delegates developed the concept of Extreme Usability, which "makes usability practitioners first-class citizens in the process, codesigners along with the developers and users". This superbly catch-phrase worthy philosophy, that ensures the user experience gets as much attention as program functionality, is well worth getting a handle on.
More information on the fruits of FLOSSing is available on the up-to-date FLOSS wiki.