I really enjoy hearing experienced vocalists doing versions of songs by younger artists. This happened a lot in the seventies, when singers, with Frank Sinatra leading the way, began to cover artists such as the Beatles and Stevie Wonder, having realized that some of the best songwriters of that time were the ones working in rock and r&b groups. I think the same thing is happening now to some degree, as serious jazz musicians and singers continue to look to the modern rock repertoire for inspiring material. One of my favourite examples of the phenomenon is the great jazz singer Mark Murphy's version of Coldplay's "What If", from his 2007 masterpiece, Love Is What Stays: http://www.youtube.com/watch?v=EVVSlcMjAJo. It's wonderfully arranged and played, and, of course, sung with his usual combination of head and heart.