You do not want to be in the middle of the back row!
Being at the back per se is not so bad, I like the last few rows where the seats are in twos, as you get quite a bit of extra space between the window seat and the cabin wall. If you're travelling Y as a couple I think they're the best 747 seats as you're guaranteed no-one next to you. Even on your own in a window seat you only need disturb one person to get up.