From the moment my wife started watching the show with me, she already hated Walt. She didn't watch season 1 at all - when you couldn't help but feel sorry for him - so that probably plays heavily into her perception, but I was always rooting for him. Somehow, even up through the end of Season 4 and the poisoning of Brock I still rooted for him.
I think the turning point for me was the scene in one of the tented houses where Walt is cooking and Jesse basically tells him he can't do it anymore and he has to go home. He's devastated by the killing of the Sharp kid and he doesn't know if he could go on. Walt says he's broken up about it too, but as soon as Jesse leaves the tent he's going about his business and starts whistling like he's happy and carefree. After that, I've pretty much wanted him to die.
Then again, who knows, maybe upcoming events will make me change my mind, lol!
Meh. It's a TV show. If I've gotten this far, I'm rooting for the bad guy who makes meth and kills people.