Control+I returns character 9, which has no usage at all. Could be easily replaced.
ASCII character 9, aka Tab, which is actually a very useful thing to be able to type even if mIRC doesn't display it as a tab.
As I mentioned in the thread Mentality linked, some clients already interpret mIRC's reverse control code as italic, personally I'd rather see that used instead (or at least as an option) seeing as reverse colours is pretty much useless.
