Sorry to up this post but I really think there's something very unexpected with the new Font class added to AS3 and which came with CS4.
The point is that JSFL method myTextObject.setTextAttr("face", "MyEmbeddedFont*") doesn't work at all on CS4 but it does work on CS3 (I didn't check on CS5).
What I want to point out here is totally specific to embedded fonts: change the textfield's font for a system font (ex: Times New Roman) through the upper JSFL instruction works perfectly fine on CS3 and CS4.
I'm very disappointed by this issue and would be very grateful if someone could give me a hand to understand why.
Please see the full issue description here : http://forums.adobe.com/message/3305797#3305797