[chryuop]

I read books in Japanese (which of course are written in vertical) and I don't see the problem. Even though I am European and thus not used to vertical writing, I have to say that reading Japanese vertical is not all hard.
Japanese works with ideograms, thus 1 symbol 1 word (I know that is simplified alot) and that makes so you don't have to read 12 or 13 letters to realize what word you are reading. You read a kanji and you know what it is, then you read the related kana that complete the meaning of the phrase.

I don't speak arabic, but I would assume reading it would be harder since you have spelled word to read in a different order.