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 understand—even given everything I just said, I’m still not convinced that I do—and that there are often surprises lurking for anyone who goes looking into the far corners of how it happens. As I’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.”