Originally Posted by exaltedwombat
You can always use inline style code for one-off formatting requirements.
But DON'T GET COMPLICATED! If your book is going to be any use, it must work on a range of devices. For instance, the Nexus 7 is becoming very popular. A commonly-chosen eBook reader for it, Aldiko, seems to ignore quite a lot of stylesheet instructions. It's often best to simply pour in your text, surround it by <p> tags, and let the device decide how it displays.
I think this may speak to which tags and css to use. If it is critical and will look bad without it, do it another way. If it is merely nice and can get ignored, why not put it in for those readers that can use it.
The catch is the now seemingly infinite number of readers and the lack of preview software for every single one of them (like grains of sand on the seashore!)