More image rehabilitation with Oprah?
I'll look for the video later (now added below), but the script of the brief promo goes something like this:
Opens with camera on Letterman: "This is the worstParty Ever"
Oprah: "Now Dave, Be Nice"
Leno: "Oh, he's just saying that because I'm here"
Letterman: (in mock Jay Leno voice): "Oh, he's just saying that because I'm here."
Update: good background on the ad from the LA Times (including Leno flying to NY and sneaking into the Ed Sullivan Theater unnoticed in a hoodie, sunglasses and a fake mustache. Here's an even more in-depth background from Bill Carter at The New York Times.