Thanks for bringing this up. I was also thinking recently about packages and how to find them and how to make sense of them (see the thread What can we do to make Julia grow fast? - #12 by PetrKryslUCSD and the recently started Is there any interest in creating a FEM Julia organization? - #12 by PetrKryslUCSD).
I believe that organizations as groupings of packages of similar nature are an organic way of organizing the ecosystem. When one is interested in finding whether there is a package does this and that it is effective to start with a brief list of organizations, identify the organization that deals with the subject, and then drill down the hierarchy to find out which packages are available. The current list of packages on the Julia website is not very helpful, especially given the sometimes quirky and terse descriptions…