What about MultiWidget ability?
Once I put your widget in one of my sidebars, it disappears from the available widgets section.
So I tried to put the <?php ad_buttons(); ?> in for my sidebars (I have multiple, one for the homepage, one for pages, one for blog entries, and one for video entries) and it messes up the sidebar for some reason.
So is there any multiwidget functionality in your plugins future perhaps? 🙂 Would make it a lot easier to implement for those of us with multiple sidebars.