Is there a way to hide the pasteboard in Illustrator CS5 so I only see whats in the
You can get a very quick, non destructive view of just the artboard area using the Navigator:
Go to Window -> Navigator and turn it on.
It's not as handy as InDesign's Preview or Presentation modes, but is is pretty handy.
EDIT: In response to @Scott's comment, here are sample screen shots of how my custom [F9] key shortcut looks in practice.
Before: Lots of stuff outside the artboard:
After: I press [F9] and artboard flotsam be gone!
Hacking the Navigator in this way is not perfect, but it does the trick and is virtually instant.