I know it's only anecdotal, but my mom doesn't get it. She's not super interested in her iPad and basically only uses it when she has to or for FaceTime. She'd be the perfect test subject for stress testing UIs and more interfaces than you'd think are doing a pretty poor job of explaining themselves. Not many icons are intuitive, hiding something in modal windows, muscle memory/dexterity and precision are all problem areas.

The hamburger is basically all of that rolled into one button. It's pretty abstract, you never know what's behind it and when they get fancy with animations and swipe gestures, it's almost always a failure.

I know it's a convenient way to clean up a screen, but the content in that menu needs to be absolutely optional for it to work.