Here's a working sample:
The following blog offered a series of very convincing arguments that led me to use flash.utils.getTimer() to build the Stopwatch demonstrated above.
The component constantly resets the time based on when it is made visible/invisible (click here twice to see it get reset +/-). If your components show a custom busy / loading skin rather than just a simple busy cursor, then you can leverage this component to also track how long your activities usually take visually.
Here's the source code: