"We know one of the most successful forms of e-learning is collaborative learning done online through social interactive discussion. Weblogs build off of this successful model as a dynamic form of e-learning content and an engaging e-learning experience." - from Blown Away by RSS Feeds & Blogs by Paul Stacey (2003).
Blogs (aka weblogs) take many forms, but a blog typically resembles an online diary - except that entries need not be of a personal nature and that there are usually many links to other online content (e.g. other blogs). Collaboration happens through blogs in at least five ways:
Different blogging tools (see the section on blogging services) differ in how well they support these different forms of collaboration - e.g., LiveJournal is (apparently) good at encouraging the creation of small circles of friendly blogs. There is also a generic tool (Trackback) that facilitates such connections (see also the section on Trackback).
Where to start reading
There is no shortage of background material on blogging. Probably the best starting points are S�bastien Paquet's article on Personal knowledge publishing and its uses in research followed by Sebastian Fiedler's Personal Webpublishing as a reflective conversational tool for self-organized learning. Both these articles discuss not only the technology of blogging, but how it relates to philosophical and political issues around web publishing and learning more generally.
There is another useful intro article by James Branum. It gives a fairly comprehensive background to blogging from a journalism perspective, together with an overview of how various mass communication theories might apply to blogging.
Another intro to blogs. An interesting 7-step process for getting grassroots knowledge management going via blogs. More grassroots knowledge management via blogs and storytelling. And another article on knowledge logging aka k-logging.
Blogs in education
Portfolios
Portfolios are not usually thought of as collaboration tools, but when they are posted on an intranet or the internet as electronic portfolios they open up spaces for collaborative work. A good intro article on electronic portfolios (including a large listing of portfolio tools) here.
Learning journals
Similarly, learning journals, are usually seen as individual learning tools, but can equally be used in a collaborative online environment. An article on Journal writing as an adult learning tool by Sandra Kerka discusses issues such as privacy and evaluation, leaning towards saying students should feel free to write about private issues and to criticise the course/lecturer without fear of lecturer evaluation. In an online journal privacy is of course not possible, but the constraining effects of evaluation may be reduced by having it occur in the context of a community of learners who read and comment on each others' journals - rather than one-sided lecturer evaluation. Kerka also discusses various dimensions on which journals could be evaluated.
Defining blogging
S�bastien Paquet maintains a collection of definitions of blogging.