Comment 38 for bug 274146

As per today's desktop team meeting, the consensus is to provide a script for the migration:

if either the logout applet or the old fusa is configured, do:
  * delete the session button
  * add new fusa into the corner
  * delete old fusa before doing that if it's used in the config

Michael has a prototype for this script already which just needs some tweaks.

This should be wrapped into an interactive upgrading hook, which explains the merging of the two applets, and offers the user to do the migration. The note should point out that this is an one-way migration and thus your configuration will not work any more on earlier Ubuntu installations.