As I understand this, it shouldn't be primarily for close friends, but for other people. For example, some journalist wrote a very interesting article, so I sent him an email, he answered, maybe we exchanged one more email, and that was it. Now with this system I would get a reminder 6 months later to reach him again. Why not? It can develop into online friendship or something good can happen out of it. If I don't do it, just nothing happens with that person anymore. And if I tell myself that I don't need to contact this journalist anymore, then ok, I will not put him into the system.
Still, I would be curious to learn how many people he has in his system.