My recent obsession with PSY's GANGNAM STYLE and a conversation with friends about music in French made me think of all of the songs I've danced/bopped my head/sung along to without knowing what in the world the singers were saying. Given the popularity of English-language music worldwide, I'm sure I'm not alone - there are kids in South America singing along to Justin Bieber not really understanding the words coming out of his mouth - but I think it's super rare for that to happen here in the U.S., partly because we're generally not as exposed to world music.
I didn't grow up in the U.S., and I had quite a few friends who didn't speak English. As a kid, I found it hysterical to listen them sing along to their favorite Duran Duran song, because they thought it sounded just like what Simon Le Bon was saying, and to me it sounded like complete gibberish. Unfairly, they couldn't in turn laugh at me when I sang in Spanish - well, except to laugh at how horrible a singer I was. The great equalizer was when a song in a language than none of us spoke became popular - then we all sang along with our own nonsensical lyrics.