I am really in favor of plugins that a) do what they're supposed to do and b) do that without overhead/clutter. That's exactly what this plugin does so here go *****!
Two things, one of which is really subjective / personal preference:
A) The text box for the ad codes is a tat too wide and therefore overlaps (Firefox 22). Nothing serious of course, just a minor thing.
B) I prefer plugins that do not ad their icon unless it is a real "menu-plugin" = a lot of sub-categories / options that demand such an icon. You could easily revert to a placement within "settings > XYZ" but then again this doesn't hurt that much...
Keep it up!