Morning Show Wars: Good Morning America Guest Host Katie Couric Takes on Today's Meredith Vieira; Next Up: Sarah Palin

Morning slugfest begins as former Today cohost sits in with her onetime rival, and Meredith Vieira returns to NBC's airwaves

The first salvo in this week's incredibly hyped, incredibly contentious morning-show wars was fired this morning, as one-time resident Today show perkfest Katie Couric took her talents over to rival Good Morning America.

Her debut—she fills in for a spring-breaking Robin Roberts all week—came just as Today's other former cohost, Meredith Vieira, just happened to drop by her old Today haunt, and one day before Couric will face off against the woman whose name she made (and, lest we forget, not in a good way): Sarah Palin.

So, how'd Couric do?

Just as she always has—there's a reason this woman lasted on morning television for so long.

Wasting no time in commiserating with cohost George Stephanopoulos about her oh-so-early call time, Couric showed she lost none of her perkiness during her foray into the evening-news game.

"I'm happy to be here," Couric said. "It's a little strange, truth be told, and my heart's beating really quickly right now."

Little wonder, as it's been a full six years since Couric signed off from Today.

"I first woke up at 1:15 this morning," she said. "I have to be honest with you, getting up this early was a lot harder than I remembered."

With that, the GMA team cued up the first of many comedy bits and references to the historic morning.

Meanwhile, over on the rival NBC airwaves, the Today team was fighting fire with fire, bringing on Vieira for an announcement that she, along with former cohort Matt Lauer and Bob Costas, will be the face of the network's 2012 London Olympic Games coverage this summer.

Which is nothing compared to what they have planned for tomorrow, when Palin will serve as the show's guest cohost. (Talk about must-see TV.)

As for CBS, they, too, got in on the game this morning, as Gayle King interviewed BFF Oprah Winfrey, who admitted to some regret involving her fledgling new network, OWN.

"Had I known it was this difficult, I might have done something else," she said. "I didn't think it was going to be easy, but...if I knew then what I know now, I might have made different choices. If I were writing a book about it, I could call the book 101 Mistakes."

Nice try, This Morning, but you're gonna have to do better than that this week if you really want to compete.