Usability in my opinion is not a matter of tools, but their usage.
Flash can be good if it is used according to usability criteria.
The Web is traditionally a silent medium. Whenever you incorporate sound into Macromedia Flash content you might consider letting the user have the option of turning it off before the sound starts playing. When using sound, make sure that its essential to the goal or offer. Remember that many computers in corporate settings do not have the ability to play sounds. News, reviews and interviews and more.