Automatically create a post for new user, only allow access to that post

Automatically create a post for new user, only allow access to that post

I saw this question being answered with a very interesting idea, namely to create a corresponding post whenever a user is being created. This allows me to create custom taxonomies for that custom post type and then let me group users together and let me query lists based on taxonomy terms. The created post can then be used as the users profile.
The code written by @MikeSchinkel works beautifully, all I would need now is disallow all other posts except the one created for them upon registration. All my users have the role of "Subscriber".
I'm looking for other solutions than custom taxonomies for the "user grouping" since I can't get it to play nice, see my question about those here.