In general, this task can be time consuming but it does depend on the skin you are working with. For instance, some skins use images for border and shading elements. Usually, these images are specific heights and widths so if you change the width of the elements using the images, things will not look right.
The Styleshout-Coolwater skin is one of those that uses images for border and shading. Not to say that this can't be done with that skin, but it would take a considerable amount of work.
I hope this helps shed some light on the subject.