Why use XMPP: native clients vs generic IM alternatives

XMPP, the eXtensible Messaging and Presence Protocol (translation: open IM) rocks. It has a rich feature set. It's well designed. And as a bit of a security nut I especially like that it supports strong encryption and uses a decentralized, federated protocol like e-mail. Anyone can install their own Jabber server (like TurnKey ejabberd). That way private conversations within your domain never leave the security of a server under your direct control. Just like e-mail.