Here. If you haven't noticed, the Longhorn SDK site on MSDN  has a new area at the bottom of each page. We call the entries in this area "annotations." This area is broken up into three parts:
1. Microsoft "official" annotations, like what you'd find in a ReadMe, but associated with the specific piece of content itself
2. General group discussion, like in a newsgroup, but again, associated with the content itself
3. 3rd party annotations
The 3rd part come from a client-side component that acts as an RSS aggregator, pulling annotations for a specific piece of content from the RSS feeds that you subscribe to via the component.
O'Reilly was nice enough to provide an RSS feed at the launch of the annotations project to both demonstrate it's usefulness and provide real annotations to about 50 pieces of content on the Longhorn SDK. In addition, they've posted a nice article about how other 3rd parties can provide their own annotations via RSS to nestle at the bottom of the MS Longhorn SDK content.
If you'd like to provide annotations for folks to subscribe to as "annotations," you can do so without any permission or special support from MS. If you'd like to be considered as a "Recommend" source of annotations, drop me an email: firstname.lastname@example.org.