U2's first single from their releases generally is their biggest hit (Pride, With or Without You, Desire, Discotheque, Beautiful Day, Vertigo) from the album. The one time a strategy of giving the song away could have worked was with "The Fly" as that wasn't the most radio-friendly song and was really a way of showing the world that U2 had changed directions. If U2 have another "Fly" on this future album, meaning a great album track but one that isn't all that radio-friendly, then releasing it as a "free" track could indeed be a great way to advertise the album. In conjuction with that "free" release, they could release a far more radio-friendly song as their true first single. This double whammy (great radio-friendly track plus free song) could give them a huge boost on iTunes (download the radio-friendly song and get the other song for free) and give fans a chance to hear 2 songs from the upcoming album. This could be a great marketing idea as it could give U2 a top 10 hit on the charts, while also showing they are savvy with the idea of sharing music for "free".