This article from the journal Language and Learning Technology looks at blogs and wikis specifically from the perspective of language learning, though its key points are fairly universal. The abstract:
Language professionals have embraced the world of collaborative opportunities the Internet has introduced. Many tools — e-mail, discussion forums, chat — are by now familiar to many language teachers. Recent innovations — blogs, wikis and RSS feeds — may be less familiar but offer powerful opportunities for online collaboration for both language professionals and learners. The underlying technology of the new tools is XML (“extensible markup language”) which separates content from formatting, encourages use of meta-data, and enables machine processing of Internet documents. The latter is key in the ability to link automatically disparate documents of interest to individuals or groups. The new collaborative opportunities this enables have led some to consider the growing importance of XML as the signal of the arrival of the second-generation Web.
By Bob Godwin-Jones.