The flex 3 sdk doesn’t support the fl packages that ship w/ Flash CS3 (includes fl.transitions.Tween and fl.transitions.easing). That seems to leave Flex’s mx.transitions.Tween class or any custom classes out there. What would be the benefit of one over the other? I’m considering Tweener b/c it appears to be simple yet flexible and AS3 capable.

Tweener (Official Site) – http://code.google.com/p/tweener/

Language Reference - http://hosted.zeh.com.br/tweener/docs/en-us/