Be aggregated as you would aggregate unto others
There should be a word for Web 2.0 services that are open in the sense that they allow you to aggregate content from other sources but that are closed in the sense that they don't expose content in forms suitable for downstream aggregation by others.
Perhaps the 'real sharing' vs. 'fake sharing' labels referred to a while back suffice?
Facebook is a good example...
Facebook is great for aggregating content from other sources, pulling it all together nicely in a single place. For example, I have recently experimented with using Blastfeed to aggregate my two current blogs (this one and ArtsPlace SL) into a single feed that can be used as a source for my Notes area on Facebook. (Note that this could probably be done more flexibly using Yahoo Pipes, something I'll experiment with in due course).
But, as Pete said in reply to my previous Facebook posting, Facebook appears to be pretty much useless if you want to expose any content you upload into it (photo albums, wall writings, notes, etc.) for aggregation by other services. For example, I'd love to be able to 'read' Facebook using Bloglines, as a simple way of keeping track of what is happening.
Pete and I have recently joined the Atom/RSS Feeds for Facebook group in Facebook - a group dedicated to improving this situation. I'm keeping my fingers crossed.