Network Monitor is a new feature available only in Flash Builder 4 Premium. Basically it helps you to see what is happening when you run your Flex project and you request data using services such as RemoteObject, HTTPService, WebService etc. You can inspect the request and response body, and you can see how long it takes for a particular request to be answered. I think these capabilities are pretty useful for determining performances issues or bugs.
I wrongly assumed that Network Monitor will work only for services created using DCD wizards. Actually it works for all services, it doesn’t matter how you’ve created them.Here is a screenshot with Network Monitor and a project that uses RemoteObjects to connect to a PHP server:
There is another feature called Test Operation that allows you to ahhh, test an operation :D. This feature only works with DCD generated services.