Anyone try center backs this way???????........

Ok, all my input is hearsay--Generally the room is the weakest part of your system. I would say this may add some 'spice'--but not accurate 'spice'---33 years ago I had Bose901s and hung them on lamp chain. (High up and near each corner)That means 16 drivers facing the wall. I could lay down on the floor and listen to the music coming from beind me. It was a fun novelty. aka spice.

I did it once when I did not have appropriate stands. If you're going for the rear ambiance sort of thing, it works. I would tend not to want to do this for multichannel hirez audio, where fidelity is more important.

Years ago, in a small living room, I had the rear surround speakers up high, but facing toward the ceiling. This was with a DPL setup, but it sounded quite nice.

If you are using cheap receiver and cheap speakers this may (and does in some rooms) work very well. It gives a more diffuse soundfield in the rear if you are sitting in close proximity to the surround speakers.

For good mid-fi or high-end components this is likely less than ideal. The reflected sound from walls is altered by the wall surface. If you are depending on this reflected sound for the entire volume of information from the speaker (rather than only some of the information as in bi/mono-pole or electrostat)you are never going to hear the details that these more resolving speakers are capable of. However "monitors" are not always going to give you wide dispersion which is what you want in a surround.

Flip-side is that if the room sucks try anything you can to create the illusion of good sound regardless of equipment quality.

Yes, I guess it would be something in the order of... Spice.