This piece is a couple years old and looks at the "decline" of Wikipedia. The author notes that Wikipedia's group of core editors has dropped from 51,000 at its peak to 31,000 by the writing of the article. One reason is the move from a new, open, collaborative source to an established, well-regulated source. Simonite quotes findings from Halfaker et al., snidely remarking that Wikipedia should change its motto from "the encyclopedia that anyone can edit" to "the encyclopedia that anyone who understands the norms, socializes him or herself, dodges the impersonal wall of semi-automated rejection and still wants to voluntarily contribute his or her time and energy can edit."
To me, this brings up questions about collaboration. Who is allowed to collaborate? On what problems? And what environments allow for this collaboration? As Harris suggested, playing with collaboration and the digital humanities might require the ability to "fail." Did Wikipedia lose this ability once it became popular and started to be seen as a replacement or equal to the "old school" encyclopedias it was supposed to replace?
Also, in the rush to think of Web 2.0 as collaborative, Simonite quotes Clay Shirky advising that "collaboration" is not the same as "aggregation." And the collaborative effort of multiple people coming together on the Web for a goal is realtivley rare. Rather, much of the Web 2.0 work is an aggregation of people's individual thoughts and ideas. Is it okay to think of collaboration as aggregation or vice versa?