Allow output as an Excel file or a table that lists circle sizes and grid locations.
This suggestion is similar to the "Color by size" suggestion below.
"This feature would help those that are using your Rasterbator to create templates for other projects ( like this: http://imgur.com/gallery/qEpis ) ...so that it is easy to judge how big or small a circle is without having to measure it."
No measuring would be needed in this case as the circle sizes would be listed.
Using a text based file would eliminate the need for a finite number of sizes that would be needed in order to match each size to a different color in the above suggestion.
I assume this information is already being generated to create the Rastorbation anyway. I'm simply suggesting the end user be able to access it directly.
Do a google search on "stippleGen" :)