iTunes seems to have different 'modes' hidden inside of it. None of them are useful for unlocking, jailbreaking, etc. This is more of a fun article, just because we are tinkering around with something that we should not be. :)
You will need to restart iTunes after changing these settings.
This is an initial study compiled by Chronic.
Turning them off (READ)
In any of the parts of this article that show a command used to turn on an iTunes mode via terminal, then to turn them off, all you have to do is replace YES in that command with NO (1 with 0 for Windows).
Store Activation Mode
This mode is flipped on by default for the iTunes versions that are in Apple stores and official carrier stores of iPhone 3G to activate the phone. It serves no real use on a home computer with iTunes installed, since you need to activate in-store anyway.
Mac: defaults write com.apple.iTunes StoreActivationMode -boolean YES Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt StoreActivationMode 1
Store Genius Mode
This is simply used at the Genius Bar in Apple Stores so that nothing gets synced to your iPhone, I guess...all this will do is take away every tab when you dock an iPhone except for the summary tab.
Mac: defaults write com.apple.iTunes StoreGeniusMode -boolean YES Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt StoreGeniusMode 1
Store Demo Mode
This has not yet been tested that much and was newly found in the GM version of iTunes 7.7. At first glance, it has no visible effect. It might not really do anything, who knows, but you are free to test it out :)
Mac: defaults write com.apple.iTunes iTunesStoreDemoMode -boolean YES Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt iTunesStoreDemoMode 1
Device Backups Disabled
This is not really a 'mode', per se, but it gets really annoying, and almost unbearable when you are trying to sync a jailbroken iPhone. You could always disable sync, but that is just a hassle for when you want to put some new music/ringtones/applications/etc. onto your iPhone
Mac: defaults write com.apple.iTunes DeviceBackupsDisabled -boolean YES Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt DeviceBackupsDisabled 1
Alternatively, to disable only automatic backups (every time you sync after connecting the iPhone), go into the iTunes settings, select "Devices", and uncheck "Prevent iPod and iPhones from syncing automatically".
Nike Kiosk Mode
This mode has been included since iTunes 7.7.1. Syncing is not permitted under this mode. Judging by the name, it's probably meant for Nike stores (to pitch the Nike+?).
Mac: defaults write com.apple.iTunes NikeKioskMode -boolean YES Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt NikeKioskMode 1
Carrier Test Mode
In this mode, iTunes will allow you to select iTunes Carrier files when you Shift / Option click on an iPhone. This allows you to restore Carrier Settings (.ipcc files) from any carrier providing they are signed by Apple (on a non-jailbroken iPhone).
Mac: defaults write com.apple.iTunes carrier-testing -bool TRUE Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt carrier-testing 1
NB: to undo Mac one, replace 'TRUE' with 'FALSE'
Disable Ping Drop-Down
Although you can disable the Ping sidebar in iTunes, the Ping dropdown next to all of your media cannot. However, you can turn it off through the command line.
Mac: defaults write com.apple.iTunes hide-ping-dropdown -bool TRUE Win: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt hide-ping-dropdown 1
There are really no point to these, as far as I can see but if you find something useful in any of these modes that I have looked over, you are more than welcome to add to what I have wrote, since after all, that is the point of this wiki :) Also, if you find any new modes in iTunes that I missed, or they are in a post-7.7 version, you are strongly encouraged to add them on :)