I am sure all the Flex/Air developers might have to use text area most of the times when you are building an application. Text area control with dynamic height seems not be an issue in normal cases but if the height needs to calculated based on text in the control then we need to think. I had the same requirement. Of course no SCROLLS.
I extended mx.controls.TextArea and here is what I did quickly.
This worked for me.Maybe there is a better way to do this. Let me know if you have tried this in a different way