Here’s a short post on why I think Facebook allowing you to make your status updates public won’t affect Twitter as much as some might think. (In order to get Facebook statuses, you no longer need to use a session ID to access statuses).
1. Twitter totally changed the model in social networks. Previously the model had been “friend” someone. Facebook requires consent for “following”. Twitter totally switched it to “Follow”. The model was now – at least if your updates were public – opt in, not opt out. That meant that public Twitter accounts could spread much faster than Facebook ones, since Facebook accounts are set to default to closed.
2. Twitter is “mainstreaming” the Follow model faster than Facebook. Facebook’s users are not used to this at all. They may well find Twitter easier to understand than changing the way they use Facebook already. What you do on Facebook is often quite different. Twitter is much more about communication/conversation.
3. Facebook’s business model is predicated on them owning your social graph. You might think you own it, but they do, in effect. Twitter has flourished by giving life to an eco-system of other services which can tell you lots of interesting things about your social graph, via their API. (One of the coolest ones lately is Twittersheep).
4. @replies on Twitter are almost always public. That’s powerful. @replies on Facebook won’t be because so much of your social graph will probably stay closed (that’s my view at least).