After upgrading to JIRA 6.4, we chose the 'Disable project navigation for all users' option as the new feature was just too much to swallow at the time.
We would now like to re-enable the Project Navigation, but have the users default to 'off' until they are individually ready to see it.
(I've seen this question asked many times over the last few months, in different ways, but it seems no one answers.)