I think this is a very libertarian notion that misses out on the social aspects of reputation. What you claim about yourself is often less valuable to a third party than what someone else claims about you. Perhaps you could store signed endorsements made by other people. But then you need support for revocation, and what about negative claims? Free speech includes the ability to say negative things about others.

Social software is very complicated because of issues like this. Something like a personal dropbox is straightforward - single customer, no community. You only have to worry about people hacking you, not what they do to each other. Anyone who gets into social software inevitably sets themselves up for making rules and judging disputes, and that often requires hard decisions.

Or compare email with social messaging; the rights and responsibilities are different and it's due to the software. Personal servers only support setting ground rules in a certain way (for example, the inability to revoke or prevent copies). Centralized services can support communities with different rules, for better or worse.