"The only band that matters." Those words were thrust upon The Clash upon the release of "London Calling," when the punk legends were at the height of their powers. While The Clash's stand as rock's most important band was brief, they did have an enormous impact on a little group from Dublin, Ireland, known as U2. Since The Clash's demise, U2--Paul "Bono" Hewson, Dave "The Edge" Evans, Adam Clayton, and Larry Mullen, Jr.--is one of the few rock acts in the world that managed to "matter" during the '80s, '90s and into '00s. Whether it's shilling iPods (now Blackberrys), trying to save the world one small gesture at a time, or delving into sonic experimentation with their longtime producer pals Brian Eno and Daniel Lanois, U2 has had an undeniable impact on not only music, but popular culture.

Yet there are signs U2's influence may be faltering. "No Line On The Horizon," the band's most recent release, has failed to yield a mainstream hit single; "Get On Your Boots" reached No. 5 on Billboard's Modern Rock Tracks, but failed to crossover to the pop chart, stalling at No. 37 on The Hot 100. And, with sales of 1 million copies in the US, according to Nielsen SoundScan, "No Line On The Horizon" is the band's weakest-selling effort since SoundScan began tracking sales data in 1991. By comparison, the band's polarizing 1997 effort "Pop" has sold 1.5 million copies, according to SoundScan.

Still, U2 remains a juggernaut in the concert arena--or, in the case of its current trek, on the stadium circuit. The band topped Pollstar's recently released 2009 third-quarter ticket-sales chart with sales of 2.3 million ducats, besting such perennial best-sellers as AC/DC, Bruce Springsteen, Coldplay and Madonna.

As the band rolls out additional dates on its groundbreaking 360 Tour, LiveDaily thought we'd check out U2's impact by asking various musicians (from the legendary Quincy Jones and Rock and Roll Hall of Famer Doug Clifford to up-and-comers like electronic sensation RJD2 and rising indie band Portugal The Man) and assorted music-industry types if U2 still matters and why.

Quincy Jones, legendary producer/arranger, entertainment mogul

"Are you kidding me? I just went to a show of theirs in New York that seemed like it had 200,000 people in attendance! They had the audience in the palm of their hand, and, most importantly, they showed their care for the world. Their relevance transcends music--it's almost like its own belief system, which is probably why those four dudes have stayed together for so long. On a side note, I just want to point out that my knowledge of Da Vinci wouldn't be remotely the same without Bono."

(In honor of Jones' attendance at U2's Giants Stadium show on Sept. 23, Bono slipped in a few lines from Michael Jackson's "Don't Stop 'Til You Get Enough," which was produced by Jones.)

Ray Waddell, Billboard, senior touring editor

"I think it's pretty obvious U2 matters and could make a case as the most 'important' rock band in the world, if demand and creativity are the barometers. They continue to push themselves artistically, both in the studio and through innovative, ambitious touring. They are in the uppermost echelon of artists in terms of global demand, rarefied air occupied only by The Rolling Stones. U2 are currently touring with a production unlike any before, playing to packed stadiums in a 360-degree configuration all over the world, setting attendance records all over the place. The staging and video are pretty mind blowing, but do not overwhelm the band, which is playing in top form. They open with several songs from the new album and the crowds instantly embrace the new material. By the time they wrap the tour next year, U2 360 will be one of the biggest tours ever in terms of both gross and attendance. I think they can continue to do this as long as they want to do it."