I doubt it's much different. Sure, the content itself is more invisible, but social dynamics are probably a more important factor to spread. I know if I notice my wife engrossed in something on her phone or computer, I'm gonna ask her what she's found just out of sheer curiosity, and that's if she doesn't bring it up first. Conversely, if I'm fascinated by something, I'm gonna tell my wife (even if she doesn't care, much to her chagrin), and I'm gonna tell 'errbody who I think might have even a passing interest. Maybe we are unique in this regard, but I suspect not, given the success of everything from StumbleUpon to Delicious to Facebook...humans are just wired to share with each other.