Hey, Sorry for the shameless self-promotion, but I'd really leave to have your opinions on this : http://blog.superfeedr.com/gospel/pubsubhubbub/synchronization/pubsubhubbub-for-synchronization/
We haven't seen yet how far we can go with PubSubHubbub. Syncing data accross the web is a big change for me. I want to elaborate more on this. Let me your thoughts. Cheers, Julien
