When you login to Gmail (or other popular web services) from Safari, you may be prompted to add the account to Mail, Calendar, Contacts, and other programs that Apple bundles with Macs. While very helpful for home users, this can be a problem for schools. Students and faculty could potentially have many gigabytes of data in Gmail, making the login process take longer and using up limited server space.
With more and more schools moving to Google Apps For Education, this is becoming a more common issue. Depending on your system, it could also mean longer waits during login and logout. If you store user data on a server, its also a lot of unnecessary disk space used (and used again in your backup system.)
To prevent this, I wrote the following script and included it in my Mac setup process inside Deploy Studio. If you use it in your environment, replace "YOUR-DOMAIN-HERE" with your Google Apps domain or remove it. If you want to disable the "Add Account" prompt for a service not listed in this script, just add it after "yahoo.com" in quotation marks.
defaults write /Library/Preferences/com.apple.Safari DomainsToNeverSetUp -array "YOUR-DOMAIN-HERE" "google.com" "me.com" "aol.com" "facebook.com" "flickr.com" "twitter.com" "vimeo.com" "yahoo.com"
If your Macs are already in service and you don't want to image them again, this script will still work. Just push it to them and run it as the user "root". You can do this in Apple Remote Desktop, Casper, FileWave, Munki (as a postflight script in a PKG installer), or other tools.