I understand the basics of Itzanami, as long as I don't think about it too hard. I don't understand how the Uchiha could possibly have spammed it as much as Itachi implies (to the point where they fight about who spammed it better!). If it costs them an eye every time they used Itzanagi, wouldn't the clan soon be reduced to a bunch of blind, bumbling morons.
Also, I thought this technique was unique to the Mangekyo(sp?) Sharingan, and I also thought that only 3 - 4 Uchiha ever activated that level of eye technique. Where could all these Itzanagi users possibly be coming from? Hell, that was the most confusing part of the chapter for me :-/