Originally Posted by Peter Sorotokin
This is very true (although, I'd say this is CSS problem in general - it is not much easier with DTBook, for instance) and I see a lot of friction there as devices start to utilize user stylesheets more. Note that doing blind overrides (e.g. overriding justify or font on p element) is not very good solution because some parts of the book may require particular style: for instance, poetry and code samples should be left-justified and math formulas typically require a specific font. What is needed is a guide on how to author documents so that user stylesheets can selectively override only things which are meant to be overridable.
Actually there is a guide like that. Authors should not define those things that the user should have control over. This is spelled out very well for Mobipocket format and could easily be adopted for ePUB.