What effect does Penguin or an over optimization penalty have?

Does a rank for a keyword drop... a few points? Hundreds? Or does the page just stop ranking for that keyword?

Does the rank for a page for a specific keyword disappear, and another page (not optimized for that same keyword) will now start ranking for that keyword but the rank is much lower?

Would like to see what other people notice about their rankings and the effects of a penalty.

It's not as simple as just saying your rank for a keyword drops but also determining if after the drop the wrong page; un-optimized for the target keyword now ranks. What to do next when we see this behavior.

Thank you.