Big news of the day is that the Xcode 4 developer preview is now open to all registered Apple developers not just those that attended WWDC. You can download (assuming you are a registered developer) from the iPhone Dev Center (look on the iOS SDK beta page).
Since this is still pre-release software I will assume it is covered by the usual Apple NDA. One thing I would say is to follow the usual precautions if you are going to install any beta software. Xcode 4 is not yet ready for production so should not be installed to
/Developer (I guess I am not giving away any secrets by saying that the default install is