Two key extra elements to add to this:
#1: The National Youth Agency has commissioned research into how Youth Work should respond to the growth of Social Networking. The first stage of that research was a survey and I'm taking a quick break from writing up the results to type this... so they should be available soon...
More details on the research at http://blogs.nya.org.uk/ywsn/
#2: Plans are starting to form for an informal gathering/conference on Saturday May 17th to bring together the many discussions around this topic.
Details at http://www.timdavies.org.uk/2008/02/14/developing-barcampukyouthonline
The event will be run along the style of a 'BarCamp' participant organised conference - so do get in touch if you'd like to be involved in shaping that gathering.