If you're evaluating StreamInsight you should know that it's more than just an API for writing streaming queries. Included with the StreamInsight installation are powerful tools that allow you to manage, monitor, tune, and troubleshoot your streaming data applications. These tools range from diagnostic methods and properties built into the API to a full graphical debugging application.
To read more, see the TechNet Wiki article, StreamInsight: More Than Just an API.
The StreamInsight Team