That's a great point - I think it does make it a lot better when there's some kind of connection between a physical movement and the response from the app. The worst kind of swiping gestures are the ones where you have to get it just right, and then a menu "magically" appears out of nowhere.

I think another possible way of indicating the presence of a gesture might be through clever use of shading - for example, a subtle gradient on the edge of the screen where you can swipe, giving you the impression that there's something "just off the screen". I haven't actually seen this in an app yet - not sure why this isn't done more, especially for the Pull To Refresh trick.