Wikipedia — can open source be a good source?

Over on Web4Lib, there’s been a bit of discussion based on this article, in which a school librarian says that Wikipedia, a popular online encyclopedia built by a community of web users, is not an authoritative source and is therefore untrustworthy.

Some of the questions raised on Web4Lib were: who makes the determination that a source is authoritative? How do they reach that conclusion? Can a community-built encyclopedia be equated with the latest World Book?

Wikipedia is immensely popular at the community college where I work and students use it all the time. Do other librarians use/recommend/hate/revile this resource?