Maybe offtopic, but I am surprised to see that pt/em is being used, while pt is meant more for dead accurate print (print css) and px is for dead accurate pixels on a screen (visual monitor thats in pixels). Em is just silly, ignore it.
The only reason not to use px is because IE6 (of course) has a bug or maybe it's a feature, and can't be resized by the end-user. But if you're on IE6, you accept you can't do a lot. The text will still display. If you want a modern browser that can zoom in on content, get one ..
px however, no matter what os, what browser, 14 pixels == 14 pixels .. It's only different when parent/child inheriting in blocks and line-height might differ a tiny bit.