Every mail server, every news server, every blog is a little island that runs on it's own. I would bet that behind the scenes even the big IM networks are actually a mountain of small, effectively independent, service providing systems that understand how to talk to each other - that's certainly how the XMPP/gTalk network functions.

This is only possible because all of those designs are fundamentally highly parallel - if your communication method has data dependencies (real or the result of bad design) that cannot be managed in that way then you get something that won't scale.

I said scaling Twitter must be a hard problem, and that it will involve correcting their implementation rather than any one magic bullet. I said nothing about IM, email, blogs, etc.

You've decided that I'm talking about something that I am not.