One of the advantages of the Web 2.0 applications is that they propitiate and make possible interaction between their users.
As a teacher I particularly think that interaction and cooperation between learners make the learning process more meaningful. Now if this interaction and cooperation is done via technology, there may be a high possibility of learning success.
Blogging is actually the basic activity of updating a blog with information and make it available on the web. (Sharp Colmer & Thomas, 2005). This of course cannot be done without the web 2.0.
Blogs have become very popular web tools as they can be used for a variety of purposes. They may serve as personal diaries to keep a record of actions. They can be used for business and trade. They can also focus on particular subjects in which people with same interests can share and interchange ideas.
In the TEFL contexts blogs have countless uses. They indeed complement and harmonize the foreign or second language teaching/learning process by promoting the interaction, cooperation and collaboration among all those involved.
Reference: Sharp Colmer & Thomas T.,(2005) "The Senior's Guide to Internet".