I just read some of the work by Martin Kloos in The Netherlands, who wrote a thesis on the use of blogs, wikis and social bookmarking in learning, in communities of practice. Fortunately I read Dutch so I am working my way through it and it it brings up a number of questions. Link
I am also working on some research amongst my MA in Lifelong Learning group that worked on the module 'ICT and Society' this term. They have used a group blog, a group wiki and made extensive use of del.icio.us. I will soon report back on this.