Since no one else has mentioned it, ICS has improved how you navigate among apps.
The three omnipresent buttons are now back, home, and recent apps. Recent apps pulls up a visual stack of everything you've used recently, so the ICS expectation would be that users would hit that key if they want to navigate among apps.
The three omnipresent buttons are now back, home, and recent apps. Recent apps pulls up a visual stack of everything you've used recently, so the ICS expectation would be that users would hit that key if they want to navigate among apps.