If you plan on doing game development for iPhone/iPad, I would not recommend using Flash CS5. I have been using AS3 for several years and found it does not translate well to iOS.
You will most likely have an uphill battle with performance which may cause problems when it comes to app submission time.
(Check out app store submission guidelines)
stadium.weblogsinc.com/engadget/files/
app-store-
guidelines.pdf
I would agree in saying check out Unity. I believe Battle Heart was made with Unity (one of my fav. games on iPad at the moment, I hope you find it inspiring!).
Also, Cocos2D has also been recommended to me repeatedly for game development.
About | cocos2d for iPhone
Hope this helps.
Cheers,
- Brad