Google has announced a new service called Sidewiki that allows users to contribute extra information to any website. It's a sidebar pane that sits alongside your browser, and you can write comments that'll appear to anyone else viewing, as well as read other people's entries.

Those entries are ranked by an algorith that tries to detect the most useful, high-quality entries. Google says: "It takes into account feedback from you and other users, previous entries made by the same author and many other signals we developed".

If you comment on a particular snippet of text, then it'll display that comment on any other pages that feature that snippet of text - A useful solution to the problems of spamblogs and sites that take content without attribution. It'll also recommend other sites of relevance.

To get access to Sidewiki, you'll need Internet Explorer or Firefox and the Google toolbar. The company says that it's working on integrating it into its Chrome browser, too, and for anyone else there's an API that's available to pull the content out and use it in other ways.

The service is available now on IE and Firefox, we'll keep you posted of its availability within Chrome.