I've been expecting someone to make this move sooner or later, and I got the impression that Posterous' Spaces was trying to do something like this (but I haven

I've been expecting someone to make this move sooner or later, and I got the impression that Posterous' Spaces was trying to do something like this (but I haven't used it much). It reminds me of adding tags to blog posts and then having subdomains for different tags