I’m currently working on a project that involves using Apache Shindig. As you may know Shindig relies heavily on caching. While generally a good thing caching is a pain during development. See my post at the Avisi blog on how to disable this in Shindig.
Xobni offers an OpenSocial container inside Outlook. One example of a useful gadget (at least one that I can relate to) is the JIRA gadget.