I guess if you look at it this way, then Geeklog's permission system is more group-based. E.g. when you think of an organization, group members can share content with other group members. But the individual member doesn't have much say in who's going to see the content, unless they are the group's admin. So you could probably set things up such that each user has their own group - but that's only really managable for a small amount of users.
Alternatively, you could go with a multi-install (a bit like WordPress MU), but that would mean that each user had their own site.
Or maybe try the
blog plugin - but I don't really know how much control it gives users over their content.
bye, Dirk