The London Scrutiny Network have indeed recently set up a Community of Practice, but not in competition with this forum! Our 'CoP' is designed to centrally store agendas & papers for meetings (rather than circulating large emails to a distribution list which is always outdated), and to discuss documents through the 'wiki' function, allowing anyone involved to edit content. The CoP does involve a forum section but this is used to further any discussion held at network meetings, with relevant forum posts here on the CfPS site being linked to.
I do find the CoP approach to be a useful single point for our network, but think the CfPS forum is still the best site at present for discussing The Big Scrutiny Issues (and to hear about Ed's favourite pieces of legislation). Haven't tried Linkedin yet, only just getting round to the 140 characters of scrutiny goodness on Twitter