Facebook adds @mentions to status updates.
thenextweb.com
thenextweb.com
http://www.techcrunchit.com/2009/05/05/rest-in-peace-rss/
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Twitter's advantage is still very distinct: public, compact thought streams that can be easily sliced and diced.
So why is Twitter in trouble? Facebook has semi-public, disparate data that is difficult to parse
Their users - they expect privacy. Facebook, like its predecessors, is a walled garden.
I don't think that will happen.
I'm a huge fan.