Currently, Ender Chests are not player-specific in SMP, such that all Ender Chests in the world, no matter who placed them, have the same alterable inventory that can be accessed by anyone with an Ender Chest. I personally am certainly hoping that they are made Player-specific for when the update finally comes out, otherwise the utility of them would be severely diminished, imo, which would be sad considering how expensive the recipe is.