Part of the aim of this site is that we build up an archive of all .Astronomy talks and hacks for reference. For the first .Astronomy conference in Cardiff proceedings were produced (I still have some if you want a copy!). For the second and third events no proceedings were produced: they take a very long time to make and are so rapidly out of date that we never got around to it. They are also easily replaced by a website, hence the new dotastronomy.com.
At .Astronomy 4 Chris Lintott (I think?) came up with the idea of producing a document following each event (beginning with the most recent in Heidelberg), that would be collaboratively written and then shared via the arXiv. The first of these is being written right now, and will be posted here when it is ready. If you would like to be involved in that process, please sign up for the mailing list.
I think it was David Hogg that came up with the name ‘unproceedings’, which I rather like and seems to have stuck