Jeremie Miller wrote a popular open source IM server and created a specification for the protocol which has been widely implemented in several different languages (Erlang, C, Python to name a few) for both client and server.
Many of the functions solved by XMPP (instant messaging, presence, federation) fit nicely into the distributed social network problem domain.
So that's why I have confidence that he knows what he's doing. Nits like "I don't like different XML namespaces" more or less miss the forest for the trees.
You mention that XMPP is widely implemented on the server, but only a few of the implementations are actually any good. To make matters worse, some of the best server implementations are written in fringe languages (Erlang for example).
I think that XMPP would be more successful if it had been more developer friendly.
I'm impressed by how elegant the protocol is. I hate XMPP, but telehash gives me faith.
Does not compute.
Using document markup as a packet based message protocol is just perverse.
I think the protocol is actually quite nice, I have an aversion to anything XML but that's just a personal preference. Have you used it in development? It works quite well... I know it sucks for binary data but that's not what it's designed for.
edit: I made my comment before axod edited in the last line "Using document markup as a packet based message protocol is just perverse." I somewhat agree with his point so ignore my reply.
I agree it's probably pointless, but I find it odd that XMPP is now apparently 'cool'. I thought it was commonly thought to be an abomination of the highest order.
Cobol is in production all over the place.
Autocracy... okay, there was that whole Egypt thing, but you get the idea.
It's a tribute to the simplicity of IRC that you can write a channel logging bot in like 20 lines of shell (https://github.com/acg/logbot).