A friend wrote to ask: Is there a way to turn off Expose without opening System Preferences, clicking on each drop-down menu and selecting the -- option? Because sometimes I just don't need it. Or it confuses my Mother. Or my advisor.
To be clear, she knows that she could go to System Preferences > Exposé & Spaces, then click on the Exposé tab, and change the keyboard shortcut for All Windows, Application windows, Show Desktop for Exposé, and Hide and show to -- but that's a whole lot of clicks, and isn't very convenient.
You could also go to System Preferences > Keyboard > Keyboard Shortcuts and uncheck the boxes, which is also inconvenient.
First I'm going to answer the question that you asked, and then I'm going to give you a few other suggestions.
Go to /Applications/Utilities/Terminal.app and enter these three lines:
defaults write com.apple.dock mcx-expose-disabled -bool true defaults write com.apple.dashboard mcx-disabled -boolean YES killall Dock
Do that before you hand your computer off and your friends, relatives, and advisors will be incrementally less likely to be confused by your computer.
There's only one thing wrong with this plan: it doesn't seem to work for Application Windows. I tested this on my regular account and the OS X Guest account, and the above commands successfully nullified F9 (All Windows), F11 (Show Desktop), and F12 (Dashboard), but F10 (Application Windows) still worked, even after issuing these commands. I have no explanation for this other than assuming it is a bug in OS X 10.6.2.
Once you get your computer back again, paste these three lines into Terminal to undo the changes:
defaults write com.apple.dock mcx-expose-disabled -bool false defaults write com.apple.dashboard mcx-disabled -boolean NO killall Dock
Ok, I've answered the question you asked, right? Now I'm going to give you two other suggestion, no extra charge.
Alternative #1: System Preferences > Exposé & Spaces, then click on the Exposé, and then change the keyboard shortcuts to require that the command key (that's the key with the ⌘ on it) be held down before in order to trigger the F9-F12 shortcuts. You can do this by clicking-and-holding the dropdown for each key, and then pressing the command key. You will see the ⌘ logo appear. It's much less likely that whoever borrows your computer will accidentally invoke Exposé or Dashboard if it requires two keyboard shortcuts. The trade-off is that you have to retrain yourself to use them as well. This probably won't take as long as you suspect.
Alternative #2: If you don't want to worry about Terminal commands or relearning any keyboard commands, take my advice and go for this option: create another account. Now I know someone is going to say "But OS X already has a Guest Account! I'll just use that!" The problem with the Guest account is that its preferences are deleted every time you logout. I'm going to suggest a "Friend" account instead. It's simple, and you'll thank me later.
Go to System Preferences > Accounts. Click the lock icon at the bottom left. Type in your password. Click the "+" button. A new panel will open up asking you to create a new account. Change "Standard" to "Managed with Parental Controls" from the dropdown. Name the account "Friend" and give it a simple password (or none at all).
When you have finished creating the account, make sure that "Allow user to administer this computer" is not checked. Then click the "Open Parental Controls" and check the box next to "Only allow selected applications" and then uncheck everything except iWork, Safari, iChat (maybe), and just about nothing else. Ok, maybe QuickTime Player.
Now there is another key step: login to the "Friend" account. You will find some applications which automatically want to run and you will be given the option to authorize them once, or for every time. Use the account for an hour or two, and authorize all the apps that you find you need for web browsing and basic word processing, which is what most guests will need to do.
You could make a regular standard account and not disable any applications. If the above steps sound too restrictive, just make a standard account. That will protect you from them doing too much damage.
Once you have an account setup, log into it and make sure the applications that someone is likely to want are on the Dock (Safari, iWork, etc). Go into the preference settings and disable the keyboard shortcuts for Exposé and Dashboard.