The special issue of Episteme (Vol. 6 No.1) on the epistemology of mass collaboration is currently available free - though not sure for how long. Not surprisingly the examples cited are Wikipedia-heavy even as major changes are being proposed.

A quick and dirty run-down of the articles:

'Wikipedia and the Epistemology of Testimony' by Toffelsen - how do people reliably know stuff by discussing it with other people rather than necessarily observing or experiencing it themselves? Take that, hard-core empiricism!

'Web 2.0 vs the Semantic Web' by Floridi - why will efforts by dispersed, imperfect humans to make the Web intelligible succeed while efforts to automate the processing of semantic content will fail? NEEDZ MOAR POWDERFUL A.I.Z?

'The Epistemic Cultures of Science and Wikipedia' by Wray - What are the different goals, social norms and incentive structures between Science with a capital S and Wikipedia (capitalized just because it is a proper noun)? Especially when comparing apples and oranges.

'The Fate of Expertise After Wikipedia' by Sanger - LOL is this just a shameless Citizendium plug?

'On Trusting Wikipedia' by Magnus - It's not just how knowledge is produced on Wikipedia but how it is read/used. I think Michel de Certeau said something like this, in general, best. Though the Onion also had a great shot at it.

'Prediction markets' by Bragues - How can we Digg for better divinations of the future? Put your money where your mouth/keyboard/mouse is!

Of course, the flippant two-liners above do the articles a great disservice and you should read them for yourself. BTW can anyone recommend a good introductory text to the philosophy of knowledge?