I have a very nice sleeping bag which has been kept stuffed as compressed as possible in a backpack for a couple of months. After reading about the negative effects of such actions, I was wondering if there was anything I could do to return it to its original poofy-ness.
Original Poofiness (or OP as they call it in the 'wood) will always be illusive. No matter how you care for your bag, it is on a steady decline toward compression from the moment you buy it.
To attempt to re-gain some loft, you need to separate the fill so the fibers or down (or whatever) that are inside can trap more air between them.
Of course, as you mention, never store a bag compressed in the first place.