I recently had Flash CS4 installed and began experiencing some issues. Specifically, I was attempting to copy a nested object from within one heavily nested frame into another movie. Flash hung immediately and never recovered.
After a little bit of Googling I found that Adobe released an update to version 10.0.2 on 5/13/2009 to address similar issues. The installation was fairly quick and painless. No reboot was required. It seemed to fix the issues I was experiencing.
You can download the update here:
If you purchased a current copy of Flash, the update is probably already included since it came out last year. The version information is on the splash page and under Help / About Adobe Flash CS4 within the application.