With all due respect, I disagree. I can certainly understand why you'd think so, but speaking as a westerner, reading manga in its original format gives me splitting headaches - it's just too hard a transition to make when you've been raised on left-to-right. Now, I am far from a manga diehard - I read them very rarely - but I do own several flipped manga, and I can't say I've ever noticed any particularly egregious hiccups in the flow of the story that it caused.