As well as the doctype, you need to look at the charset you are specifying as there may be an interaction there and also look at how your pages are being served up by the server, as html or xhtml.

Th basic principle use were using for font sizing was fine although I would set the body percentage higher so that it closely reflects any base font size that the user has set.

You can find some info on this in the css sticky at the top of the forum.