"If we're talking about children in primary school, or even in high school, will the long-term outcomes be better if they learn to interact directly with each other, or if they learn to interact by commenting on each other's weblog entries (assuming that they find the latter as engaging as dealing with other kids, an assumption I very much doubt would be valid)."I think this is probably true, but I've been thinking of a different spin on this one. If my students are working on a project to plan their futures (careers, post-secondary education, leisure, relationships, etc), and one of the goals is to get them talking to each other about those plans, you'd hope that each student could find one other that shared some interest or future goal.
If Jimmy is interested in working with lizards, studying herpetology at Utah State University, and collecting movie posters from the 1940s, he's unlikely to find someone else in the class (or school, or state) that shares any of his interests. If it's assigned, a classmate will dutifully comment on his stuff (in person or online), but there's no engagement or true exchange taking place.
The power of the network only kicks in if you open it up to the wider web, where Jimmy might connect with Suzy on the other side of the country, who happens to be fascinated by lizards and movie memorabilia -- perhaps she's never heard of the program at Utah State University, but if you connect those students, they both increase their research and knowledge base in their shared interest areas.
In a related thread, the excellent Blogtalk site (cool project) has a new article about blogs as possible lightweight e-portfolio platforms, with some good examples and background.