Earlier today Google announced the release of Sidewiki, a universal web page commenting system that allows anyone with the Google Toolbar to add comments and feedback on any web page. The web is abuzz with the news. The video included below gives a good overview of how Sidewiki works.
But that's not all. Google has also announced the release of the Sidewiki Data API (our Sidewiki API Profile), a RESTful API that allows developers to access information maintained in Sidewiki about a particular web page (or information by a particular author).
It does appear that we're starting to see a new trend with new Google product releases, wherein APIs are released concurrently with the product (there are now 55 Google APIs here). We saw this same type of open access when Google Wave was initially introduced. And this is good news for developers, as it seems that Google increasingly is considering open APIs a core part of their new products.