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. These commands can be used on Windows too, just open Command Prompt and cd to "%CommonProgramFiles%\Apple\Mobile Device Support\bin".
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
Store Activation Mode
This mode is flipped on by default for the iTunes versions that are in Apple storea and official carrier stores of iPhone 3G. Because iPhone 3G does not use the traditional method of activation, the stores activate iPhone 3Gs using this method. It serves no real use on a desktop computer with iTunes 7.7 installed, since you need to activate in store anyway.
defaults write com.apple.iTunes StoreActivationMode -boolean YES
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.
defaults write com.apple.iTunes StoreGeniusMode -boolean YES
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 :)
defaults write com.apple.iTunes iTunesStoreDemoMode -boolean YES
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
defaults write com.apple.iTunes DeviceBackupsDisabled -boolean YES
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+?).
defaults write com.apple.iTunes NikeKioskMode -boolean YES
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 :)