Stacy Schiff wrote on Wikipedia for The New Yorker's July 31 issue (so I don't know how long that link will last).
Much of the article defines Wikipedia and describes the growing number of people with responsibility for content. The thing about having credentialled people keeping an eye on things, she writes, it that "too many Wikipedians are fundamentally suspicious of experts and unjustly confident of their own opinions." They don't take well to edits and just change them back. Or, they write at length on popular that topics, one hopes, are ephemeral: "The (generally good) entry on St. Augustine is shorter than the one on Britney Spears."
Style often goes wanting, too, Schiff points out. She gives the entry on Nietzsche as an example: while "debate" leads to frequent revision of the essay, the disagreements are "over Nietzsche's politics; taken as a whole, the entry is inferior to the essay in the current Britannica, a model of its form."
Wikipedia people are quoted as predicting the doom of print encyclopedias, and in return, "Jorge Cauz, Britannica's president, told [Schiff] in an e-mail that if Wikipedia continued without some kind of editorial oversight it would 'decline into a hulking mediocre mass of uneven, unreliable, and, many times, unreadable articles.'"