The Place ability is great but is lacking in two key ways what Photoshop's Smart Objects can do – at least for my purposes.
First, and this can be worked around currently, is that I cannot edit a Placed file unless it's an .aphoto file. This seems like a simple fix because opening a JPEG and choosing Save as... does the conversion and the resulting file can be placed and edited, so the functionality is all available, just not linked. In fact, Photoshop has the ability to "convert to smart object" any layer that is already in place – doing that would solve the problem AND the related problem of the Placement having to be in an external file to start with.
Second, duplicate by reference. The ability to load one "smart object" and have multiple copies each with their own scale and translation, layer effects, etc, but when you edit one, all copies are updated. This is really useful for logo work amongst other things.
I've been watching lots of tutorials and playing around with Designer to get used to it. When I got to the video on Symbols in Designer 1.5, this concept leapt to mind, and so I made it.
It makes use of Symbols, Artboards and the power of the Export Persona to simplify outputting all the required sizes for an iOS application icon. And of course designing the artwork in the first place is easy and fun with all the Designer tools at your disposal.
This blog post explains how to use it and contains the download link.