Could we one day see the end of U2? Frontman Bono says he wouldn't be surprised if one of the four members wanted to call it quits after four decades as a band. Speaking to the UK's Q magazine, the sunglasses sporting frontman claims, "It's never been a given between the four of us that this would go on forever. U2 is a fast car. It's not meant to be cruising." Of course that time isn't likely to be soon. The Irish rockers just wrapped crisscrossing the US and are about to head out across Europe at the end of this month. Guitarist Edge says everyone in the band is having fun on the current tour. Is there a set time for a band to retire? When would that be in your opinion?