> In my opinion, the most compelling reason is that many people are there. Yes, I've seen this in action with real-world groups that form a Facebook group to r

> In my opinion, the most compelling reason is that many people are there. Yes, I've seen this in action with real-world groups that form a Facebook group to replace a mailing list, or ( shudder ) a Yahoo Group. 99.99% of their recipients are already on Facebook, it's free-at-point-of-use and it supports group functions. So they go ahead, freezing-out the ones who aren't on Facebook with quotes like 'just create an account, it's free'. I'd join Facebook if I could pay a subscription fee each month so as not to be analysed and advertised-to, just to rejoin many groups that have moved there.