I´m not sure this is where I should post this, and I´m not absolutely sure nobody has done it before (although I couldn't find anything).
I wrote a widget that implements a button + label and functions as a drag-drop target. The main point of the widget is that it's compatible with the AceConfig 'type="input"'. Ok, when I say I wrote it, that is actually an exaggeration. Most of the code is drawn from one or another existing AceGUI widget.
I mainly did this because it seemed a lot easier than implementing my entire configuration frame manually just because I needed a drop target button.
The source file includes a full AceConfig example in the comments, for extra ease of use.
Basically, set, get and validate all take or pass an itemString for items and spells, or "macro:nn" for macros.
Is there any place where useful (I think) widgets can be put for general use? If not, well, if anyone is interested they can pm me and I'll get them the code.