One thing that came up in discussion was whether or not anyone has ever done any economic impact studies on Wikipedia and other community-produced open data and open content projects (OpenStreetMap, other Wikimedia projects etc.)? If civic society groups like Wikimedians, OpenStreetMappers, MySociety.org people etc. want to convince governments to put more data out, it'd be helpful to show the economic effects of this, or to have people who are trying to convince government to put the data out to have access to this kind of information so they can make better decisions (cue cynicism here).
There is a basic problem here in that it's difficult to account for non-traded goods. Since no-one pays for Wikipedia, the value to the economy appears to be zero.
An alternative methodology would be to account for the value that would be required to replace Wikipedia if it didn't exist. As an example of this methodology you could take the traded price of a Wikipedia substitute (e.g. Britannica Online is £50 a year) and multiply that by the number of users, which I'd estimate at 30 million in the UK. So the hidden value to the UK economy of Wikipedia could be as high as £1.5 billion every year....
But this might not be the most helpful answer to you. :-)
Chris