Even polished writers screw up who v. whom, so much so that the prescriptive rules on it may change.
I found a good illustration of proper usage of who v. whom from MMAFighting.com of all places:
Frank Mir's longstanding grudge with Brock Lesnar shows no signs of dissipating, and in a radio interview last week, Mir raised the stakes by saying that if he gets a third fight with Lesnar, he'll be motivated by a desire to break Lesnar's neck and see him die in the Octagon.
"A lot of individuals are so worried about being politically correct," Mir said in an interview with Mark Madden on WXDX radio. "I'd rather go ahead and say what's on my mind than to sit there and come up with some PC 'Oh, the guy is a great fighter and I have a lot of respect for him.' If I don't mean it, why is it even coming out of my mouth? ... I want to fight Lesnar. I hate who he is as a person. I want to break his neck in the ring. I want him to be the first person that dies due to Octagon-related injuries. That's what's going through my mind."
Those comments are unfortunate, and they don't reflect the good sportsmanship that Mir usually espouses. Perhaps Mir is just trying to play up his rivalry with Lesnar, but he says he truly hates Lesnar, whom he beat in 2008 and who beat him in 2009.