I noticed this issue a few years ago while animating something (something brilliant, I'm sure) and realized while describing it recently that most people don't actually think about the "behind the scenes" stuff when creating set driven keys. So here's a video describing it!
In short it goes over the "interpretation" graph that gets made when a set driven key is created and how the tangents (and shape generally) of that curve affect your animation.
Please to enjoy . . .
Maya/Rigging: Set Driven Key Animation Problems from zeth willie on Vimeo.