The iOS 4.0 gold master SDK (not release candidate) is now available for download from Apple. All members of Apple's developer program (not just paid members) can access the iOS 4.0 SDK, with its enhanced APIs. As in the past, the ongoing NDA for the iPhone version of iOS 4.0 is expected to be revoked as the GM is put out for public developer consumption.
So what's next? Apple is expected to put its latest iPad iOS 4 SDK into beta soon as well as the new Game Center functionality. Meanwhile, developers are anxiously anticipating the general beta of the new Xcode 4.0. If you are a paid or online developer and you haven't watched the Developer Tools State of the Union, you really should head on over to do so at your earliest convenience. It's an amazingly exciting time to be developing for iOS and Mac OS X.