Id never heard of <aside> i had to google it. it doesnt seem like anything I'd ever expect to encounter in an epub though - would ADE even have a clue what to do with it?
So I think I'll just go on happily nuking everything beginning with <a !
I have an HTML5 cuick guide on my tablet so lets see what else there is in its index for a:
acronym - though its says that is now unsupported
address
article - new for html 5