Apple’s developer website is back up, and there’s iOS 4.1 GM seed ready to be downloaded in there.
If you’ve got a developer account, you can find it here: https://developer.apple.com/iphone/index.action
The 4.1 GM built should come with HDR features (announced at today’s keynote) available for iPhone 4 users and Game Center (sort of active). Please let us know about it in the comments. Still no sign of iOS 4.2 beta for iPad (due in November).