There has been a lot of work related to Participatory or Public Participation GIS (P*GIS I guess) in the academia. There are numerous examples of people doing amazing work introducing GIS outside the confines it was residing thus far. From getting community organizations to use GIS, to getting every day people to perform GIS analysis for various purposes, P*GIS has seen tremendous work thus far. We have indeed reached a stage in which a single component of GIS has become participatory, but more remain.
I am again following definitions of GIS that can be found everywhere. Basically, GIS is defined as a combination of three following main components: data, processes and output, all controlled by specific actors (or users if you may). The P*GIS thus far has been concentrated on the output, the production of visual displays by not a specific actor but rather the public, as well as the initial goal statement of what is to be produced. And this is why I argue that P*GIS has not yet reached a maturity level as described in the early days of P*GIS. But there is a lot of hope in the horizon.
The idea of data as a component of P*GIS has found a cozy home in what is termed Volunteer Geographic Information (VGI). The VGI idea comes within academia as a response to the widespread introduction of user-generated data to web-based mapping solutions, like Google Earth/Maps. The VGI literature discusses the collection of data by individuals, out of their own interest, to supplement data generated by other agents (either government or private agents). A good example is OpenStreetMap (website), a collaboration of individuals from across the globe to collect street network data to compete with commercial offerings. While this is not directed toward a specific sort of analysis, there are multiple uses for it, limited only to the imagination of the analyst.
The idea of processing as component of P*GIS has seen some work done by GIS services. There are numerous examples of either free, or commercial services offered. Geocoder.us (website) offers one basic GIS service: geocoding. Google, through its web APIs provides geocoding services as well,along with a route-finding algorithm. ESRI introduced the commercial ArcGIS Server, which provides the full functionality of their GIS software through a network, which is not restricted to the data on their servers like Google’s solution. These are just few of the examples of GIS processing functionality provided as a service to the public, either for free or a fee. But this is where P*GIS finds its other component.
Therefore, while there are different areas of research focusing on participation on processes, there is no unified P*GIS yet. And this is the opportunity. To combine (or mash) the capabilities built by these diverse actors into one, truly participatory, GIS.