Oops, I meant point sizes, not pixel sizes. It's probably little difference anyway, they're both absolute measurements.
I could use percentage sizes too.
The percentage sizes would give you some flexibility would it not? It is basically setting a “fraction” of default size.
I have not used them in my limited experience. My brother and father are the Web-designers/programmers in the firm.
I checked some sites out and I found one dealing with CSS directly that was using font-size: em.
http://www.yourhtmlsource.com/styles.css