Just to summarize, it separates the concepts of "line height" and "font height" so that you can define the former, and use any font with equal or less line height to equal effect.
I really think it's a beneficial feature. It has been argued that viewports will allow the same effect, but I think this is a much more efficien way to do it, and it will still have benefit once viewports are around. Many of the WPSes in our gallery, as well as included ones, benefit from the use of this patch as it allows significantly increased freedom of font choice while using them.
