Hi Chris, the transform palette options in Publisher are quite basic, I cannot see a percentage value - this is much more useful when scaling objects which regularly comes up in our workflow.
For example: if you have multiple images of different dimensions and/or formats and you want to scale them all to say 50% or 25% of their original size - please see attached screen grab from Indesign to explain this.
Nearly all design software both 2D and 3D has a scale factor function in either 'percentage' or decimal value 'scale up or down by a factor of 1.5 or 0.5' ..surely Publisher has this and I'm just not seeing it!?
You can scale to a percentage of the *current* size by typing something like 50% into the width/height fields in the transform panel. This does not represent a percentage of the *original* size but of the size at the time you enter the percentage.
Percentage of original size is not currently possible in Publisher from what I understand.