I use it pretty much all the time, though mostly the "double-click home button" to fast switch between applications. Most apps seem to support fast switching (where I don't have to wait for them to re-initalize), though a few don't.

Otherwise it is helpful if I'm doing AirPlay to my speaker system from Pandora or the iPod... or if I'm downloading in the background (app updates or podcasts, or whatnot).