What I'm curious about is how they'll present this to users who try to install an unsigned application the first time. Will they educate the user, and provide a way to get to the Settings and change it if they want? Or will they present it in such a way that 90% of users give up and assume the installer is broken.
Remember that most Mac apps don't have an installer - they're self-contained, and installing consists of extracting the DMG and putting the app on your hard drive.
The notification will probably take the same form as the error message you get upon trying to launch a PowerPC app on 10.6 without Rosetta installed.
TO be fair, even apps without an installer will open a warning dialogue the first time it's actually run letting the user know this is an application that's "new" and hasn't been run before.
Also - as long as Apple makes it easy for developers to get signing keys, which seems to be their direction as far as OS X goes, there's no reason for developers to complain about it too much. Just sign your builds, and you probably avoid any warning message.
Just as long as they don't present it the way Windows does - pretty much the same dialog boxes but one has a blue banner (signed) and one has a yellow banner (unsigned).
