Where is the preferences file for the Adobe Application Manager Update Notifier menubar app?
If Adobe behaved itself it'd have an option in the Login Items under Apple > System Preferences > Accounts. But it's worth keeping that in mind for other apps you may want to prevent from logging in.

As for disabling Adobe Application Manager, you actually need to create a com.adobe.AdobeUpdater.Admin.plist file in your user's Library Preferences folder. The easiest way to do this is using the Terminal.

Follow these steps:


Launch Terminal app (usually found in your Utilities folder within the Applications folder)
Once it opens, copy and paste the following command:

defaults write com.adobe.AdobeUpdater.Admin Disable.Update -bool yes
Press return


Now the plist file should be created and Adobe Update Manager should no longer launch when you login.