From what I have gathered, Open Space Technology is pretty much the “unconference”, and I would even say that the STF workshops in Armenia, Georgia and Egypt employed the very same technology. However, the OST does not offer the solution to document the informal, in-between-sessions proceedings. Hence the community journalists would be a great option. But then again, there should be a decision on what data do we want to collect? If a journalist reports some meeting, group discussion - we get her/his interpretation of what was happening. And it is enough for a curious outsider or for anyone who was involved in another conversation/discussion etc. But for qualitative research purposes the raw information (a basic transcript) is more useful: it is richer primary data, that can be used not only for content, but also for deeper discourse analysis. On the other hand, it is less interesting for those, who want just a few bullet points to summarize everything.
My suggestion would be to have a few people, who will do transcripts as well as summaries of discussions. For privacy purposes the names/surnames/nicknames/anything that can identify a person should be withheld from the published transcript (unless the people agree with it), but some sociological data could be available for the researchers upon request (only for statistical/descriptive purposes). And then the transcript can be summarized in a few bullet points for more general use. It just seem like a double work, but for example, when I need to write an article, I transcribe interviews at first, and then work the raw text into a nice story. So in this case, no story, just a short summary and/or bullet points would not be a big burden.
diaries are common tools of ethnographers. You record not only your interviews, but also personal observations, various events, emotions etc. Of course, conferences do not last for months, but I guess it would be great to have more in-depth feedback from short diaries from some of the participants, who would agree to write down what they saw, experienced, felt etc. each day in the evening, and then later submitted it to the community. How is it different from writing down after each session? Well, it takes less time, it captures the main moments of the day, and still is a more detailed feedback than just the one in the end of the conference. And I suppose the privacy issues can be worked out here as well.