Ideally we might have one server per person. There's no reason, really, why I shouldn't be able to run my webmail, media store, calendar, lightly-trafficked blog, etc. from an RPi sitting at home and just use them wherever I like.

I used to do this with Owncloud, and Sandstorm has done some cool work in this field, though ISP's of course make it challenging. Also, it does raise the risk of everyone contributing to massive botnets.