Another vote of support for clipping/layers masks - they make the process of creating multi-layered images much more streamlined and would mesh well with the workflows of many users of other art/design software. Another way they're really useful is that they're editable on the fly too, something which stencil creation isn't. Want to make an area quickly visible or masked, paint in some white or black on the layer mask - simple. Use shades of grey for variable transparency - great. Being able to lock or unlock them is really useful too - unlock the layer and reposition the masked content only, lock it to reposition the mask and content. I can't overstate how useful these sort of functions are. You just can't do this simply and quickly using stencils. Using other layers for selections works but can lead to the creation of needless amounts of layers. So yeah, pretty please...