Re: challenging the network effect.
A telling moment that happened two nights ago for me. A friend from ~8 years ago came to visit and we wanted to send a joking message out to a few people from the old group of friends we used to hang out with.
The conversation was literally:
A: "Post it to Facebook and tag everyone." B: "Ehhh. It would be funnier to find an old email thread and reply to it."
We went with B. It seemed like a better idea, plus we weren't sure if folks in the group checked Facebook. But everyone reads email -- and sure enough, we got life updates from the whole gang within 12 hours.