4 finger swipe already exists on OSX as a system wide gesture for Expose and Application switching. No, it's not exactly an apples to apples comparison as OSX doesn't depend on gestures as heavily, but the tradeoff is well worth the benefit.

You no longer need to push on a physical button to switch between apps!

Re: the container peeking through the application's interface.

This isn't necessarily a bad thing either. I'd argue that consistency can (in some cases) be more important than giving application developers total control. Have you ever been to a site which intercepts right clicks so that you can't copy and paste?