Theres a bit of a gotcha in flex if you are trying to get large, huge or massive text in your labels on flex 3. I thought it would have been as simple as specifying a large value in the css for the font but this does not work. I eventually found the answer on adobes developers forum (thanks bguijt)

In order to have larger text you just do this with your label tag.

<mx:Label fontSize="100" scaleX="2" scaleY="2" text="Hello" />

This will give you 200 size text... just keep scaling until you have the size you require.