Today the August 2009 DirectX SDK was released on MSDN, strangely enough the August SDK was released in September.
This release contains the first official release of Direct3D 11 (RTM), which was previously only a technical preview. According to the release notes, this version of Direct3D 11 will only work on the RTM version of Windows 7, not on the RC and Beta versions. So I guess only vendors and MSDN subscribers will be able to develop software until Windows 7 hits the retail market.
There’s also the issue of pure Direct3D 11 hardware not being sold yet but that should be right around the corner if the SDK is here.