Reihan Salam points me to a presentation by a Facebook executive who claims that “E-mail…is probably going away….” Well, remember Google Wave? I assume that email-as-we-know-it will evolve. But one thing I pointed out to a friend the other day: remember when you were excited to get “new mail?” (perhaps the reference will be lost on younger readers, but there was a time when it was cool and special to have an email account, and be able to receive messages from people who lived in Ecuador at digital speed) Now it’s more like, “now what!?!?!” Email is a utility through which your boss may contact you. The excitement factor has now shifted to Facebook, where old friends you’ve lost touch with may request to be your friend. But if Facebook becomes as ubiquitous as email, as taken-for-granted, you might start getting wall messages from your boss. And at that point Facebook will become a utility you’ll want to not log into, not because you want to avoid wasting time procrastinating, but because the “real world” has infected it.

Technology has been one reason we humans have by and large broken out of the Malthusian trap. But a key difference between innovation on the physical dimension (e.g., the combustion engine) and technologies which have social utility is that human psychological faculties can shift only on the margins by much smaller degrees. In theory you can have as many Facebook friends as Facebook will allow you to have; it’s a scalable phenomenon. But in reality a small circle of friends become Facebook “friends” who you barely know, because your mind isn’t geared to really keep track of so many social relations.

Of course the people who run tech companies are smart and many know this. But their jobs hinge on you becoming invested in the idea that their firm is going to Change Everything. So they’re not going to emphasize too much the fact that human utilization of technology is substrate constrained, so to speak.