Wikipedia has probably gone a long way towards popularizing the notion of "peer review" in Wikipedia's own practice and making it a normal expected practice for the large numbers of people partcipating in Wikipedia's project, particularly after Wikipedia's reliability vis-a-vis Encyclopedia Britannica became an issue that was resolved in favor of Wikipedia in Nature magazine.
Peer review results in frequent revision. Wikipedia is continually improving because continual peer review is built into Wikipedia's system of online publication: "Wikipedia articles are getting constantly better as people go back again and again to old articles to add to them, reword misleading statements, correct factual errors, etc. This means that the quality of Wikipedia articles is ever-improving." (source). Some even advocate the Wikipedia peer review process for other more formal areas like medical research pointing out its benefits:
"For readers, Wikipedia is a win. In traditional publishing, readers must wade through many articles on a subject, each written by a few experts, published at 1 moment in time. In Wikipedia you read 1 living article written by many, continually updated by many. Who needs 50 articles on avian flu when 1 will do? And Wikipedia content is often the best on the Web, which means the best anywhere.
"For writers, Wikipedia offers neither authorship, recognition, reward, nor punishment. Articles aren't indexed, but with Google and Yahoo!, who needs it? The motivation for writing is love of information and a desire to share it. I say a variant of Wikipedia for medicine is the future -- and it's good."
Alternatives to Wikipedia with stronger authorial and editorial control by experts in different topics are appearing. Nupedia, the predecessor failed because of a peer review and citation process that was too rigorous. Only time will tell whether authorship and citation can be added to online encyclopedias like Wikipedia without losing the spririt of volunteerism that drives content creation.