Apparently there's an idea for a feature to enable users to transfer their account and data from one federation node to another. Pretty sure it's in the "just an idea" phase, so don't hold your breath.
Well, with email you can a) forward from one address to another b) set up an auto-reply (I've moved), c) copy your message history via imap/maildir/mbox-files. Ditto for address book(s).
