In 2012 the Scottish Government consulted with the public on how the upcoming referendum on independence should be run. Citizen Space was the consultation platform which was used for this exercise. The process collected over 26,000 responses with each response published on the site.
It's worthwhile checking out the site to see how it was organised. The final result from the process was a document which outlines the key findings.
One of the key things that occurs to me from this exercise is the ability of Citizen Space to scale from smaller local consultations to large national interest consultations with ease.