Today's instances of sharing with social media have a long history. For example:

MUSIC SHARING
Now: Publishing a music playlist (e.g., iMix on iTunes)
Before: Creating a mix tape for a friend or blasting your boom box in the park (popping and break dancing, of course)
Past: Music (record) party at your home (1950s)

VIDEO/PHOTO SHARING
Now: YouTube/Flickr
Before: Home movies/Photo Albums
Past: Slide shows or vacation presentations

As I said before, all media is social. These sharing behaviors we see today are not new. It's reach, accessibility, usability, transparency, and recency that have changed.