Despite valiant efforts to come up with an alternative approach, pop-ups still infest the web. It seems like every site you visit wants you to sign up for a newsletter, take advantage of an offer, visit a sponsor, or provide feedback—all before you’ve actually reached the content you arrived to see.

The value of the pop-up to designers is obvious: a piece of information that doesn’t need to be on screen all the time, doesn’t need to displace other more permanent elements of the design; creating its own window gives it temporary space, and the required prominence, without interrupting the rest of the layout.

Pop-ups can easily be dismissed, often simply by clicking anywhere but on the pop-up. Psychologically they partition content, allow for competition entries, logins, and the like, to be focussed on for a short period of time. Pop-ups also neatly side-step the issue of opening new windows, maintaining a single session and preventing users from passively navigating away from a site.

But pop-ups are also intrusive. They’re a lot like a waiter that tries to take your order before you’ve taken off your jacket. They’re easy to apply to a site with minimal disruption, but easy solutions are rarely good solutions.

Usability testing tends to show that users dislike pop-ups—closing them as soon as possible—but that they also tend to understand them, perhaps because they mimic the basic UI of the OS.

With usability so high on everyone’s agenda, did pop-ups simply evolve at the right time? Are they a stable design pattern, or a particularly persistent design trend?