Alrighty, the title should say it all, but here's why.

Main reason i'm trying to do this is because i want to create an action that would allow one to select a folder with a large number of randomly sized files and apply a circular or square logo (in a Photoshop layer set) to the lower-right corner and space it away from the edges. There should be a way to do this without needing a different sized logo file for differently sized photos.

the only way i can think of to use one Photoshop layer set is to somehow create an action that can resize a layer set to match either a larger or smaller canvas while constraining proportions of that layer set.

Attached is an inset of an 8"x8" layer set at 600 dpi with a logo in the lower right corner. The bottom layer is a 50% gray Overlay and the Logo has a drop shadow applied. The idea is to get this file to work with any image size/resolution.

My fingers are now crossed.

Can you give examples of the sizes/dimensions of the images you are applying the logo to? Is there any reason you could not resize the images as a first step of your action?

for example, applying a logo to a database with FINISHED images like
8x10,5x7,4x6,4x5,3x5,2x3 - either horizontal or vertical
web images for desktops at various sizes.
these images cannot be resized or re-resolved
this is really for a studio branding workflow; i need to stamp LOTS of different pictures quickly by using a single action and a single layer set from a PSD file without having to do make an individual action set for every size/shape of photo they have.

i know it seems like the application is too broad, but it would literally be possible to do this if you didn't need to pre-size anything or re-create secondary action sets just because you need to optimize it for a different size or shape of photo.

If you're confused why there is such a large 8x8 canvas behind the logo in the corner, it makes it possible to use the bounds of a canvas to determine the relative scaling of the image whenever the entire layer-set is resized.

one of the developers on the adobe forums said all i gotta do is create a *.pdp file and use the File>place command to import an image that is larger than any canvas i plan on using. Since most of the canvases that i will print are no larger than 13"-narrow @300dpi, i just made an 8x8@600 dpi transparent canvas with my logo on it, and import using "Place..." and then finish it off by applying actions that will align it properly in the corner, give it a drop shadow and PRESTO! Too easy!

SPREAD THE WORD!!!