There is a plethora of questions where people talk about common tricks, notably this one.

However, I don't refer to commonly used shortcuts that a noob would find cool. I am talking about a seasoned unix user (be she/he a developer, admin, both, etc), who thinks (s)he knows something 99% of us never heard or dreamed about. Something that not only makes his/her work easier, but also is COOL and hackish. After all, vim resides in the most dark-corner-rich OS in the world, thus it should have intricacies that only a few privileged know about and want to share with us.