I was listening to the lastest episode of the Talk Show with guest Joanna Stern about the Apple Watch. During one section they started talking about tap as a means of communication, and the impact this might or might not have. As John wrote in his review of the watch, it's not that hard to imagine at least a few scenarios where, for example, sharing a heartbeat would be novel, intimate, and gain even widespread use.
Having thought about this more, I do wonder if perhaps the ability to effectively touch someone from afar will turn out to be a big deal. I think it will.
You can imagine that a native SDK app might even be able to take input from one person and send that to another, enabling a morse-code method of communicating, for example.
There's a lot more to consider here, but it seems like it's a bigger deal than I thought it might be at first.
It also makes me wonder just how much more intrusive it will feel to be tapped by some spammy notification in an app.