"I own the collection of comments on my blog, and you own the comments you've placed on my blog and all others. I should be able to back up a complete set of comments on my blog, and also back up a copy of all comments I've placed on all blogs."
Filters are rapidly becoming a pertinent issue for developers of social media services. Aggregation platforms are in the perfect position to lead the pack.
When you count words rather than edits most of the content in Wikipedia does indeed come from contributors outside the core, but Wikipedia does have a lot in common with traditional publishing organizations.
APML allows users to share their own personal Attention Profile in much the same way that OPML allows the exchange of reading lists between News Readers.