It should be hard to predetermine the defining moment in a mega-music extravaganza that includes an intimidating list of legendary artists, including the Rolling Stones, Bruce Springsteen, the Who, Eric Clapton, and Billy Joel. However, at New York City's charitable 12-12-12 concert, which earmarked proceeds for victims of Superstorm Sandy, talk was overwhelmingly all about one act: Paul McCartney, who would reportedly be joining the surviving members of '90s phenomenon Nirvana on stage.

The hype for this appearance was such that everyone from late Nirvana frontman Kurt Cobain's widow, Courtney Love, to industry standard publication Billboard saw fit to discuss it prior to Wednesday night's broadcast. Although former Nirvana members Dave Grohl (now frontman for the multiplatinum-selling Foo Fighters) and Krist Novoselic had, indeed, performed live together at times over the past few years, speculation continued to center upon which song Macca would deem fit to make his grunge debut upon.

The producers of the show wisely recognized the value of the gossip and saved the collaboration for the very last minutes of a nearly six-hour broadcast. By the time McCartney took the stage--way past midnight in New York--the audience was vibrating with expectation.

"Recently, some guys asked me to jam with them," McCartney finally announced to the crowd. "So I showed up, ready to jam, and in the middle of it these guys said we haven't played together in a few years...I finally understood that I was in the middle of a Nirvana reunion." He then introduced Grohl and Novoselic; as well as erstwhile Nirvana member Pat Smear, who played guitar for the band for a year prior to Cobain's 1994 suicide and currently plays in Grohl's Foo Fighters.

Kendrick Lamar fans didn't know what to expect when the "Swimming Pools" rapper tweeted that he would be performing a secret show on the corners of 12th and Figueroa in downtown Los Angeles — directly across the street from the Staples Center, home court for the Los Angeles Lakers.

PHOTOS: Kendrick Lamar - Crash Concerts

Considering this is the eve of Lamar's TDE/Aftermath/Interscope debut "good kid, m.A.A.d city," he is determined to make his Crash Concerts offering dope. "I wanted to do something special … that actually made a point, made a statement," he says during an exclusive interview with Yahoo!

"Better to do it in our hometown, right after the Laker game," he explains. "I've never done a surprise show like this."

The massive crowd spilled into the streets, exceeding the limits allowed by the city. After performing "Swimming Pools," "The Recipe," and a bonus from his "Section 80" release, the police disperse the crowd as a chopper hovers over. Yahoo! and Lamar make the evening

When Harry Shearer—of Spinal Tap and Simpsons fame—decided to bring in some vocal support for an album of satirical songs, he picked guest singers ranging from Dr. John to Jane Lynch. But for the leadoff track, "Celebrity Booze Endorser," he had no choice but to call the Fountains of Wayne hotline.

As some will recall, some years back the singer Robbie Fulks actually had a song titled "Fountains of Wayne Hotline," dedicated to the idea that there might be a number a songwriter could call when in doubt about what kind of key change to employ in a well-crafted rock tune. Shearer had already composed "Celebrity Booze Endorser" by the time he got around to dialing up FOW, but their power-pop presence still loomed over the song's creation as well as recording.

"The bands that I listen to for just pleasure and rock & roll excitement at this point in time tend to be them and XTC," says Shearer. "I wrote it with them in mind. I had been driving around in my car listening to Welcome Interstate