Also, on exit, CS5 would reliably crash with the error: “Could not save Preferences because the file is locked or you do not have the necessary access privileges”.

Fortunately, I’m not the only early adopter suffering from this problem. The issue appears to be that Adobe’s DMG installer incorrectly sets some permissions under ~/Library/Preferences.

What cleared up this issue was executing the following command ( in Applications -> Utilities -> Terminal ).

sudo chmod -R u+w ~/Library/Preferences

These are the specific directories that were errantly set to read-only after my CS5 install.

~/Library/Preferences/Adobe/Extension Manager\ CS5
~/Library/Preferences/Adobe Photoshop\ CS5\ Settings
~/Library/Preferences/ExtendScript\ Toolkit

CNet has an article mentioning other directories that can sometimes be affected. So, if setting only Preferences didn’t work, you can try the following.

sudo chmod -R u+rw ~/Library/Application\ Support
sudo chmod -R u+rw ~/Library/Adobe