I spent time with ibacco, and on his WordPress instance, the ad widgets cannot be removed once added. For example, when you try to click 'edit' on the added widget, it does not open up to show the 'remove' button.
Using firebug, I see that when clicking the widget, there is no communication back to the server. In addition, there is a JQuery error on the page:
$("myform") is null
This looks like a WordPress bug to me, but I can only reproduce it with Advertising Manager widgets.
Does anybody else have this issue?