I really don't think it's a good idea to have separate hard-coded logo image files for IE and everything else. It's already bad enough that you have to overwrite files installed as part of MediaWiki to set the logo displayed by Monobook (*separately* from the other skins), now you have to do two, and remember to do the one that your browser never shows?
It just seems like a lot of trouble to maintain.
-- brion vibber (brion @ pobox.com)