Not for people who were happily navigating with their keyboard. Not for people who were going to copy/paste anyway. Not for people who wanted to look at something in another tab before finishing your aggressively self-important webform. Not for people who will inevitably accidentally hit something in the dialog before even seeing it because they were typing too fast and it accepted their keyboard input. Not for people who will resent you on principle for stealing their focus to stop the proceedings with idiocy (google it). And certainly not for the people who are so tired of dialog boxes that they've given up on reading them altogether.

What you want: User reads your dialog box notifying them to double-check their email address.

What actually happens: User maybe looks at your dialog box just long enough to figure out what it is before clicking whatever they think will make it go away. A tiny proportion of anal-retentive users who would have never gotten it wrong in the first place actually do what you asked them to do.

http://arstechnica.com/security/2008/09/study-confirms-users...

> Follow-up questions revealed that the students seemed to find any dialog box a distraction from their assigned task; nearly half said that all they cared about was getting rid of these dialogs. The results suggest that a familiarity with Windows dialogs have bred a degree of contempt and that users simply don't care what the boxes say anymore.

http://mikepope.com/blog/DisplayBlog.aspx?permalink=480

> It's not that users are morons or that they "forget" to think. Its that users are trained to not think... dialog boxes usually say "If you want to tech the tech, you need to tech the tech with the teching tech tech. Tech the tech? Yes / No" If you press one of those buttons, something happens. If you press the other one, nothing happens. Very few users want nothing to happen -- in the majority of cases, whatever happens is what the user wanted to happen. Only in rare cases does something bad happen.

http://blogs.msdn.com/b/oldnewthing/archive/2003/09/01/54734...

> If you are trying to accomplish task A, and in the process of doing it, an unexpected dialog box B appears, you aren't going to stop and read and consider B carefully. You're going to try to find the quickest path to getting rid of dialog B. For most people, this means minimizing it or clicking "Cancel" or just plain ignoring it.

http://www.joelonsoftware.com/uibook/chapters/fog0000000062....

> This may sound a little harsh, but you'll see, when you do usability tests, that there are quite a few users who simply do not read words that you put on the screen. If you pop up an error box of any sort, they simply will not read it. This may be disconcerting to you as a programmer, because you imagine yourself as conducting a dialog with the user. Hey, user! You can't open that file, we don't support that file format! Still, experience shows that the more words you put on that dialog box, the fewer people will actually read it.

http://alistapart.com/article/neveruseawarning

> What about making the warning harder to ignore? A subtle warning will get passed by, so let’s pull out all the stops: we’ll blink the screen and play a loud stretching noise to ensure that the user is paying attention. Try as we might, it still won’t work. The more in-your-face the warning is, the faster we’ll want to get away from it (by clicking “Okay”) and the more mistakes we’ll make. The thing is, no matter how fully in-your-face the computer presents the warning, we’ll still make the same mistake—clicking “Okay” when we don’t mean to.

http://ignorethecode.net/blog/2008/10/31/nobody-reads/

> We all know that people don’t read dialog boxes, yet when there’s a problem with our UI, when people don’t understand what they’re supposed to do or when they do something wrong, we tend to try to solve the problem by adding more text to more dialog boxes.