Dynamic Help is quickly becoming one of my favorite features but it is a hidden feature for many. Dynamic Help is tied into the code hinting engine of Flex Builder, if you click on any class, method, property, or MXML Tag, it will provide results in context with the cursor. The results provide entries to the Flex API reference and Search results from the documentation. To turn on Dynamic Help simply do this: Press Menu > Help > Dynamic Help and click on any variable, method in MXML or AS3.
Turn on Dynamic Help, you will find it is a great feature.
Cheers,
ted :)
DIGG IT! 
Wicked, I LOVE IT.
Especially nice whilst still learning the API