Anyone try it yet? I'm downloading right now on my 920.
Really looking forward to Cortana and action center. Besides those two, there's a huge list of new features:
http://www.wpcentral.com/windows-phone-81-features
Here are instructions to install the beta:
•Sign up to be a Windows Phone developer at appstudio.windowsphone.com for free using the Microsoft account associated with your phone.
•Get the Preview for Developers app from the Windows Phone Store (QR code below)
•Run the app and sign in with your Microsoft account.
•Check for updates (Settings > Phone update > Check for updates) and download/install any that are available. You’ll have an update to download and install before Windows Phone 8.1 shows up if you’re downloading the Preview for Developers program for the first time.