Hi great-taste,
The size of the image in the sidebar (as well as most other formatting) is controlled by the CSS (line 283 of the pg-sas.css for image size)
You an override this in the css or move a copy of this to your theme file and it will be safe from being overridden.
I will look at making this more customisable from the settings page but that will not be in the next release.
Cheer,
Brian (PeoplesGeek)