I have always had problems with line-height. When I had 2px difference in a header between IE and Firefox, the solution was line-height. When my sIFR title was smaller in IE and bigger in Firefox, the solution was line-height.
Eric Meyer gives his thoughts about the line-height layout.
“The point here is that line layout is very difficult to truly understandâ€”even given everything I just said, Iâ€™m still not convinced that I doâ€”and that there are often surprises lurking for anyone who goes looking into the far corners of how it happens. As Iâ€™ve said before, my knowledge of what goes into the layout of lines of text imparts a sense of astonishment that any page can be successfully displayed in less than the projected age of the universe.”