Of all the tricky grammar topics, who versus whom ranks right up there: get it wrong, and you risk looking like a rube. Get it right and you risk looking pretentious. Get it wrong in a different way and you risk looking like a pretentious rube. So we at Lifehacker, who want to be both right and non-pretentious (but…
Source: LifeHacker – When to Use “Who” vs. “Whom”