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It seems that this Facebook patent covers what we were already doing in 2001/02.
I did not have time to go through the details, except reading the Slashdot story, but this patent, the way it is described in the abstract, covers what Splinder (the largest Italian blogging and community platform) was already doing in 2001/02; and BTW, Splinder was part of a US company based in NY (Tipic Inc. of which I was the co-founder and CEO).
At that time I was on the board of the Jabber Software Foundation. We had developed two services, one based on Jabber, and the other one a Blogging platform. We also developed, what we called, an event dispatcher; all the posts and comments, from the blogs hosted on the platform, were funneled to the IM system and to ad-hoc pages on the web. As a user you could subscribe to any blog, which would give you a list of the latest activity of the blogs, and if you were online with the IM, you would receive an IM message.
Some services are still available online, so you can find as much prior art as you like.
Also, Splinder was sold in late 2006 to the largest media company in Italy and is still online.
Updated: Howard mentions that we were also doing this with our Motime platform in English in 2003.