The effect I'm hearing is that highs tend to sound like they're coming from the rears, as well as some ocassional flanging.
For an album like Crash Test Dummies: God Shuffled His Feet, the main vocal sounds neither forward nor backward and the bgv's sound like they are behind you. Most cymbals, snaps, claps and anything with loads of reverb tend to come from the rears too.
I have good woofers in my front doors. I'm not missing any bass, thank goodness.
It is also the case that when I favor my system's balance all the way to the rears, the fronts are silent and the rears sound trebly and ghostly. When I begin to roll the balance back toward the front, the rears get fuller and fuller range, until zero, where they are quite full. Then, as you begin to favor the fronts, you begin to lose the surround effect, of course.