Feature Freezes: When Enough Is Enough

As highlighted during IRC discussion on the day before release of 13.04 (see http://irclogs.ubuntu.com/2013/04/24/%23ubuntu-release.html#t21:13 ) there is a need to discuss when enough is enough. When should things land in a release cycle? What should deadline enforcement look like? When features and other changes are proposed to be landed during the last two weeks (see for example: https://bugs.launchpad.net/unity/+bug/1169238 ) should there be a point where it is said that "Enough Is Enough"? After changes to the support cycle length, what is required to ensure compliance with deadlines set by the Release Managers so that a release happens with minimal incident?