Hi
I would like to suggest a feature which makes it possible to display the boundaries of elements on along with magin(s) and padding on a page visually.
Dreamveawer has this feature and I find it to be really cool as it helps when one want to get a quick overview of what is on a page and if there are any gaps between the various elements which would make them behave in an unforeseen manner.
I'll admit that it is not the most important feature, but it would sure be nice to have.