He guys,

I have read a million and one books in the course of my learning web dev that advise you that sizing fonts in ems is often the best option and in this instance , I opted to do so in order to prevent IE7 from over-sizing the fonts (a well known bug when certain types and combos of positioning are used).

I was gutted to see that opera has over-sized everything which looks so nice on all of the other browsers. My style sheet is huge and it took me an hour to change all of the font sizes (its a large CMS), can anyone explain to me what has happened and what I can do other than changing them back to px and using the old * + html rule to get IE to behave?