We have just installed our 4th ceiling using styrofoam Decorative Ceiling Tiles.  Our home was built in 1916 and all the ceilings have (had) the popcorn ceilings.  We intend to cover up every single one of them with the styrofoam tiles.  The end result is so beautiful, and the project is so incredibly easy that I pinch myself after every installation!  I have recommended the tiles to all my friends, who admire the ceiling, and then are amazed to discover that the tiles are merely styrofoam, glued over the popcorn ceiling of old.