Man, this is looking REALLY SHARP! Really nice.. It has very nice features for resizing, moving etc (specially for doing it with the keyboard which is more precise)..
A few (Future) suggestions I have (asides from the ones you listed -- nice ones) are:
-Status bar (or just a label) to show the current area of the object while moving/resizing an object (just so we don't have to double click on objects to make sure they're aligned)
-I'd suggest adding a quick "if" to prevent flickering of the image while holding down the shift or control keys
-When clicking ADD, may be we should show a list of objects we can add (from objects.txt) and allow the user to select one (because it is not as intuitive to enter the object type and number -- but it does work).
-I'd really like to see an option to create and delete .skin files -- Specially to create the headers and allow setting/editing the Skin Description name.
I did not expect anything this nice would come up so unexpectedly.. I for one, know I'll be using it a lot...
Thanks again for your very nice work on this..
EDIT: It's now easy to see how some skins have their object areas so badly defined..