Google released their new tool, that allows to annotate content on Webpages. [1] Users can contribute annotations to all Webpages. Annotations can be published, and linked (http://www.google.com/sidewiki/entry/113597143741382940941/id/oEZJa_Sto6sxBfbw1qD-yJ4eTCI) . The full potential of the protocl can be found at http://code.google.com/intl/de/apis/sidewiki/docs/2.0/developers_guide_protocol.html .
Google returns Annotations as Feeds in an atom format. A sample request for all annotations on my webpage (http://www.google.com/sidewiki/feeds/entries/webpage/http%3A%2F%2Fnm.wu.ac.at%2Fnm%2Fwirl/full)
[1]… http://www.google.com/support/toolbar/bin/static.py?hl=en&page=guide.cs&guide=24296