We have created some sample code to show how the Plugin API can be utilized. It can be found at https://github.com/aimsinnovation/examples
You can compile and run the example directly but you will need modify the App.config before running it. More information on this can be found at the GitHub link above.
The example code will show how to extract events and components from the connected BizTalk agents (ports, orchestrations, hosts etc) and their statuses.