Your Facebook Friend Just Joined
yongfook.com
yongfook.com
The article though is completely subjective. These are things that can be A/B tested very easily, and should, before making grandiose predictions about effectiveness. The author is probably like most of us here a techie and has a different relationship in regard to email. Most of your visitors might not care that the mail they receive is about a person they hardly know. It might still be very effective in getting the user back to the site, because it's very personal.
It might be even more effective for acquaintances than for good friends, because the user probably already knows his best friend is also on pinterest. Maybe the user might see this as an opportunity to get to know that person better. This whole article is just conjecture.
In the end, it's the numbers that count. If 80% of the fb friends fall in the "acquaintances" group, then pinterest, if it would self-limit to good friends, would be unable to send 80% of the mails it's sending if it would not self-limit. Sure, more people might unsubscribe from these notifications because of that 80%, but most probably don't. Why prematurely lower the amount of call to actions you have? 5% conversion for 100% of your friends joining, vs 8% conversion for 20% of your friends: even with the higher conversion, you're still losing out.
See patio11's advice on mails and how different it works than most of us here think.
Even if I was interested, sending a notification to me when they have
joined is a pointless milestone. All you are telling me is that if I click,
I get to see an empty profile.
Yes, the email notifications seem like they could be valuable but they tend to be about friends that don't mean too much too me. Great points made in this article.