>I'm getting a weird result... the line spacing gets a few pixels larger or smaller when I flip this between 0 and 4, but the font stays the same. Could it be that stylesheet is affecting this? Maybe I should influence the fontsize of the body tag, and define all other styles as percentages of it?

I tried it on Microsoft.com and it worked. However it doesn't work on UT because Michel set all the fonts/sizes in stylesheets.