Early Show co-anchor Harry Smith caught up with him, as well as cast members and the director of the night's big winner, "Slumdog Millionaire," at the Governors Ball after the show.
"You commie, homo-loving sons of guns," Penn said in accepting the hardware during the broadcast. "I did not expect this and I want it to be very clear that I do know how hard I make it to appreciate me often."
In this highly competitive category, Penn was up against Mickey Rourke in "The Wrestler," Frank Langella in "Frost/Nixon," Brad Pitt in "The Curious Case of Benjamin Button" and Richard Jenkins in "The Visitor."
Milk was the first openly gay man elected to major public office in the United States when he won a seat on the San Francisco Board of Supervisors in 1977. The following year, he was shot to death along with Mayor George Moscone by board colleague Dan White.
But during his life, he inspired gays and lesbians to stand up and come out, helped turn the Castro neighborhood into the gay Mecca it would become and roused crowds with impassioned speeches that often began with the words, "My name is Harvey Milk and I am here to recruit you."
In wrapping up his own speech, Penn mentioned the protesters who lined the streets of Hollywood near the Oscar festivities, holding anti-gay signs: "We've got to have equal rights for everyone," he said.
Backstage, when asked what he would tell those protesters if he could speak to them, Penn responded: "I'd tell them to turn in their hate card and find their better self."
Penn told Smith, "I had incredible support from a lot o people involved in this movie and people who had put their lives at stake ... in the initial campaigns of Harvey Milk, and I knew how much it meant to them, so I shared in that."
Smith admitted he wept openly during several scenes of "Milk," because, Smith said, "It really is a film about a civil rights movement."
"Yes," Penn agreed, "and I'll, say somewhat tangentially, that I felt that about several of my fellow nominees' performances, and it was a big surprise tonight because , as I said earlier, if I were a member of the Academy and were not me, I'm not sure who I would have voted for."
"Entertainment Tonight" co-anchor Mary Hart, who joined Smith for the special Early Show Oscars coverage, said Penn was just as humble at the Vanity Fair party.
"Slumdog Millionaire" grabbed eight Oscars, including best picture, and the cast was still soaking it in when Smith chatted with them.
Anil Kapoor said it was great as one award after another was announced for "Slumdog," but "the ultimate, the defining moment," was best picture and, when Steven Spielberg opened the envelope to announce the winner and said "Slum" -- "Before he could say 'Dog,' Kapoor chuckled recalling the moment for Smith, "we were all there on the stage!"
A grateful Freida Pinto observed to Smith that, "Starting from my first audition to what's happened now, I think everything has been a dream, a beautiful, beautiful dream, and I hope I have more wonderful dreams like that in the future as well!"
"Slumdog" Director Danny Boyle noted the unlikely nature of the film's booming success, saying to Smith, "Every time we've kind of met a big problem, we've embraced it and it's something you learn in India. They are into that. You don't fight your problems, you embrace them. You absorb them and open yourself to them, and you find that you benefit from them in the long term."