I find it interesting how everyone can have a different take on this book. To me the whole 2+2=5 thing means that we can be conditioned to believe what someone else wants us to believe. If you remember in the book, O'Brien tells Winston that they don't kill people who oppose Big Brother because that would make them martyrs. Instead they condition them so that they actually love Big Brother and then they are free to kill themselves if they wish. 2+2=5 was just another way to show that conditioning in effect.