Why Pinterest makes customers wait
Normally on this blog, I'm a strong advocate for making the web easier and faster. Low-effort behaviors with quick payoffs are much more likely to become habits than high-effort behaviors with delayed rewards - so an effective modern website should deliver what the user wants as fast as possible with the least possible effort.
It might seem contradictory when a new business like Pinterest comes along and succeeds by doing the exact opposite - putting new users on a waiting list for days before they can use the site. This is the beautiful thing about communication, sometimes the exact opposite of a technique can work just as well, or better, given the situation. The waiting list works, of course, through the same well known psychological mechanism that brings Black Friday shoppers to blows - scarcity. Humans have a innate psychological mechanism to covet things that are rare - particularly when others covet them. So why not make all your products scarce?
It's a truth of human behavior that we value more things that we work for - and wait for. However, we're also paradoxically less likely to do things that take time and require effort. So, once you've gotten someone to expend time and effort on something - they will value the opportunity more and experience more of a attitudinal change. The danger is they may balk and never expend the effort to begin with. So how do you know how much effort to require?
The question is complicated and depends in part on how likely a person is to complete the desired action with or without an added hoop. If you know you can get someone to jump through a hoop, the time and effort will cause them to value what you offer more, as has been shown in many psychological studies. Hoops are particularly useful in situations where people are initially compliant - but lose interest and stop complying.
If you've run a website, you know it's common for 3 out of 4 users who create accounts to use the site for 2 minutes and the never come back. This is the Morning After Effect. Strong initial compliance followed by de-valuation and boredom. Pininterest is targeting this compliance bottleneck, by making the first, easily complied with step more difficult, it makes users more likely to stick around, and form a relationship! Note, it's also important to downplay the effort / wait time (there's nothing on the site that says "Wait 5 whole days to get an account!" This way you keep initial compliance high, but introduce a delay to increase subsequent compliance.