Organically learning or creating shortcuts and gestures for arbitrary actions Keyboard shortcuts across OS X and applications are an amazing productivity booster that have proven to be worthwhile, notwithstanding the sometimes arduous task of first memorizing them.

Is there a setting, app, or hack of some sort that would allow me to go about my business as usual and display any extant key combination as actions I perform match mapped shortcuts? This would stimulate passive learning of keyboard shortcuts -- and for ones most relevant to the user no less! Keep track of my actions so that I could assign shortcuts to series of actions would really be something.

What aspects of the OS libraries available could a developer use write such software?

Something like seeing the shortcut next to the menu item, only when the menu isn't used...  e.g. something that would flash "Command + L" each time I click the address bar of a browser, or "Command + Shift + D" each time I clicked "Send" on a mail message.
Menu items contain shortcut information

Mightbe a bit obvious, but most of the menu items contain shortcut information. And if no shortcut is visible for a specific menu item, it is most certain that none is available.

When you use a menu item, do not click, but use the shortcut instead. 

You can also create you own shortcuts, but that is something different.