[Trezoid]

The tech guys at deviantart are constantly working to make the sign-up flow better and then to keep people coming back, and given the relatively large number of younger users they get it wouldn't surprise me in the slightest if they implemented that after finding a lot of people get their email addresses wrong.

As an aside, they also post fairly detailed blog posts about some of the challenges of working at the kind of scale dA faces (http://dt.deviantart.com/blog/)