Jill Walker has been redesigning her blog (the new design looks very slick by the way) and has posted on a few of the CSS tricks she has learned in the process (fonts, positioning, columns, round corners), she has found along the way. I've stolen one of them for Donutage: the Owen Briggs Universal Font Definition. Briefly, it amounts to setting
font-size on BODY to 76% and then defining all subsequent font-sizes in ems. It's meant to address the discrepencies among the base font sizes of different browsers/platforms (that, among other things, makes using ems alone problematic). As far as I can tell, it doesn't quite eliminate the difference between Mac and Windows displays (I still want to bump the size up one notch on my Mac for comfortable viewing), but it makes the difference less striking and makes the steps between different font-sizes less dramatic, so I'll be employing it from now on.