Ignoring all the issues with XMPP itself, this extension (which is referenced often by the XMPP community) doesn't seem to have many implementations. In fact, a friend tried to find even a reference implementation and found nothing. To me, this extension is complexity built on complexity. Perhaps it's worth exploring if you're married to XMPP already, but PubSubHubbub (or at least, my implementation) achieves the same thing much simpler via HTTP.
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Jeff Lindsay
http://webhooks.org -- Make the web more programmable
http://shdh.org -- A party for hackers and thinkers
http://tigdb.com -- Discover indie games
http://progrium.com -- More interesting things