|Lots of people are already signed-up||You have to get people to sign-up|
|It’s a place where people are resident a lot of the time||It’s a place people have to remember to visit|
|They already use if for other purposes||You can guide what it’s used it for|
|You have to be careful not to invade||There’s less chance of feeling invaded|
|People can feel exposed||It can feel safer|
Have I missed anything?
[Alan's FriendFeed experiment is an interesting alternative to the two - it's a new network but it's more open than Ning]