- Some sort of social-networking software that uses some sort of (xml?) standard protocol to communicate with others' instances of the software. Basically everyone runs their own Facebook profile page/wall and comments/posts are pushed between instances.
- some sort of OpenID-ish thing that integrates PGP/GPG keys for improved security
- ready to go software for running automated backups from the user's home computer (this could easily support all OSes)
If this was some sort of 'cloud server' or shared hosting plan that cost users maybe $10 or so it could work out pretty well. Though I'm not sure how the existence of current 'free' options would affect things. But I feel that such an option would be the best option for people in the long run. They would retain their own backups of their data, so it's not locked away on some company's server where they can't extract it (and the company will say 'tough luck' if all your data is lost).