It seems like there are an awful lot of "forty year old" events to commemorate this year -- events that reflected social conflict and contention and often put a spotlight on the difference between generations. Forty years ago Apollo 11 landed on the moon and the Stonewall riots took place in New York; there was Woodstock and then Altamont; the My Lai massacre and the march on Washington against the Vietnam War. The last public performance of the Beatles took place on the roof of Apple Records in 1969, and John & Yoko got married that year and the bed-ins for peace happened.
Now in 2009 Paul Taylor and Richard Morin at the Pew Research Center in a Social & Demographic Trends Report have released the results of a study, which documents that there are still big differences between younger and older adults in their values, use of technology, work ethic, and respect and tolerance for others. (79% of Americans say there is a major difference in the point of view of younger and older adults.) There is, however, one area where the generation gap does not seem to be apparent: music. And surprise, two thirds of respondents to the Pew survey say they most often listen to rock music, placing it ahead of six other genres. For every age group below 65 rock is at the top of the charts. Taylor and Morin compare these results to a 1966 national survey where rock and roll was by far the most unpopular music in the county, and 44% of adults said they disliked it.
The entire report is released at the Pew Research Center's site, and it is quite revealing to see which performers sustain popularity. (The Grateful Dead really hold their own.) See: http://pewsocialtrends.org/pubs/739/woodstock-gentler-generation-gap-music-by-age