The Dell Streak has been rooted, to allow "super user" access, from mobile phone unlocking pioneer Paul O'Brien as his site
MoDaCo. How did this happen so quickly? Paul's not going to say, but he he did reveal it was an exploit found in the device, and keeping it close to his chest may prevent Dell from patching it up in the near future. Obviously, it's unlike Dell to actively patch up flaws that allow modification of a device, but this tablet is subsidised by carriers and is unlike any other product they're ever released, so it will be interesting to see their move.
But what does this "rooting" mean? Well for the everyday user, not a lot; but for those wanting to push the boat out and really experiment with their device, a great deal indeed. With super user access you can use Apps with your phone to control elements of your phone you've not been previously able to. Things such as CPU over-clocking, WiFi Tethering (coming in Froyo anyway), root access to the file system and so on. It also means we're one very small step closer to an unofficial method of getting Android 2.2 on the Dell Streak, we're still in need of an actual ROM to load up.
Just search for "root" in the Android Market and you will see all of the interesting Apps and what they can do!
Obviously, any rooting is done at your own risk!