My company has developed a fast-growing personal data store to which we are considering added controlled access features (and others) like those discussed above. It's called Evernote and has been in invitation-only beta since late February: www.evernote.com. If anyone interested in "Data portability, privacy and personal data stores" wants to try it out and give me feedback on features, send an email request with the subject "personal data store" to feedback@evernote.com and I'll send you an invitation.