The Windows Phone Mango updates are going out to handsets, and the RTM version of the Mango SDK is now available. In addition, the Marketplace is now available on the web. Check it out here.
You can get the Windows Phone 7.1 SDK from the download center. In addition, the docs and samples have been updated and finalized for this release as well. You can check out all the docs here. If you are just getting started building apps for Mango, you might what to check out the What's New in the Windows Phone SDK.
As we look forward to future releases, we would really love your feedback about the documentation and samples. Visit the Windows Phone Documentation UserVoice site to give us your feedback and vote on issues.
Thanks and enjoy!