This strikes me as a rather explosive question, and it would be interesting to hear different viewpoints. Several years ago I think I would not have considered it as plausible as I do today. Formal networks now are competing with personal networks that people set up for themselves, both social and professional. Why join a structured professional network, when you can use a ning or Facebook to bring into your orbit the people who are important for informal learning and exchange on your preferred practice, and use google or any other search engine to find all the relevant new information for your field. What can formal networks now provide as a compelling value proposition for their members?
I guess they can be filters and aggregators, but there are lots of organization providing clearinghouses and tailored information collections. There might be a few specialised niches left to populate here, but fewer and fewer every day. Maybe they can provide quality control? But voting and ranking functions can do that to, as well as checking the popular tags on del.icio.us or the public bloglines accounts of reputable experts. What is the most compelling offer for formal networks today?
Maybe they need to go back to F2F formats, that is something that many of these new tools don’t provide. When they are virtual, then they are increasingly in a crowded space.
We are just about to kick off a meeting organized in conjunction with our international network of communication and education/learning experts on New Learning, no doubt this will be an interesting question for reflection…