I hung up the Ebony Blade on the weapon mount above the dresser on the 2nd floor, came back and it was sitting on the floor. Tried it again, and now it's completely gone. Anybody ever experience this before, maybe a fix?

Try reloading the last save, and try to hang up the Ebony Blade again. I only experienced it with the Axe of Whiterun, so I ignored the Axe, so I put it in my Weapons Dresser.

Not just PS3, and not just the Ebony Blade. Keep your artefacts in a chest. Other weapons, such as Red Eagle's Fury, have also been reported to fall off plaques. I only use them for the generally worthless crap you get for becoming Thane of places, sentimental value and all that.