Function keys not working F9

Sorry to hear about this mess!

First we'll work on getting your computer back to normal, then to the f-keys.

First, restart you computer. This may be all it takes to fix the problems. If not, go to Disk Utility (in Applications/Utilities). Select your hard drive (probably Macintosh HD) on the left. Then click Verify Disk Permissions. Let it scan your computer. If you need to, it will tell you to click Repair Disk Permissions.
Let me know if this helps. If not, see below.

To make the f-keys work as expected: Open System Preferences. Go to the Keyboard tab of the Keyboard Pane. Check the first check box, Use all F1, F2, etc. keys as standard function keys.

Snow Leopard has very, very few bugs anymore; this problem is fixable! If it doesn't go away soon on its own (be sure to try restarting, too), you can take it to the Apple Store and they'll fix it for free, since it's so new.

Let me know if this helps,
-Nate

I just got a band new iMac, and was trying to get the F9 function to work similar to my very old eMac. But it appears that F9 is not mapped and F10 is mapped to audio-Mute, F11 to quieter, and F12 to Louder.
But then I found the F keys for the brighter, dimmer, Expose, and Dashboard (F1, F2, F3, and F4), so that seemed ok.

With the aluminum keyboard, Exposé and Spaces now use F3 (Despite what is shown in the "Exposé & Spaces" system preference):

F3 All windows
Control-F3 Application windows
Command-F3 Show Desktop
Option-F3 Spaces

(Use Shift with the above keys if you are not in a hurry.)

Those keys have two functions, the ones associated with the F numbers (F1-F12) and the ones shown as icons, referred to as Media Keys.

F7-F9 as Media keys in fact control iTunes.

Nate was right, you can decide whether those keys funtion as F-keys or Media keys:

Go to the Keyboard tab of the Keyboard Pane. Check the first check box, Use all F1, F2, etc. keys as standard function keys.

Either way, you toggle their function by holding the fn key, next to the home key I believe, while you press a Media key. While holding fn, the "louder" volume key will act as F12 and bring up Dashboard. The "fast forward" key will function as F9 and trigger Exposé.

If you have checked Use all F1, F2, etc. keys as standard function keys in the keyboard system preferences, then you can temporarily access the media keys by holding the fn key while pressing them.

So the system preferences say Exposé is mapped to F9, but when you simply press that key without also holding down the fn key, you are really accessing the Media Key function of the key, not "F9".