I don't know whatever became of the first walled off kiosk at AT&T that supposedly contained the Dell Streak, but a second—much smaller—mystery display has recently been discovered by someone in our forum that is believed, again, to contain the device.
It has been said that "people from corporate" set up the display (complete with bolted down lid) before store employees arrived a few days ago and that the big reveal will take place this weekend, likely on Sunday, the 25th.
There's a video (below) taken at a different location with a 360-degree view of the display, which features the words "innovation comes to life" running down the side.
Some people think the Streak had to wait 30-32 days after the iPhone 4's release to be announced by AT&T (why only the Streak and not the Captivate, though?), which could explain why Dell is running a pre-sale without divulging information about availability, price, and carrier involvement. Another rumor hitting my inbox pretty hard right now is that AT&T-subsidized Streaks will only be available for purchase through Dell.com but that the AT&T Core Stores will have the device on display so customers can try it out first.
Thanks for sending in your theories, everyone!