I'm sure someone somewhere must have hashed this out, but is there anything worthwhile in having buddylists for webfeed aggregators? For IM they provide presence and awareness. For aggregators they might provide the basis of a permission management scheme for distribution of subscription and readership information. Oh and if the aggregator supported per item tagging that might be made available to folks as well. Users could allow their aggregator to "chat" with other useful services and agents out there on the 'Net.