It's official! Windows 8 Beta will be made available late February 2012, along with the Windows Store. The Windows Store Preview event was held in San Francisco where the app policies and business terms for the Store were announced, both of which are available in full to read at your leisure on the Dev Center. 

Windows Store for Beta Availability...

• The Windows 8 Beta along with the Windows Store for Beta will be made available late February 2012 and available to all Beta users.
• During the Windows 8 Beta, the number of developer accounts will be limited and only free apps can be submitted.
• Developers invited to our Beta will have a free two-year app submission subscription. After Beta, to sell apps in the Windows Store, developers must purchase an annual developer subscription of $49 (U.S.) for individuals, $99 (U.S.) for companies.

Windows Store - the Economics...

• Successful apps will make more money on Windows by earning 80% of every dollar of revenue earned after passing $25,000 (U.S.) in total revenue (as aggregated across all sales in every market). The first $25,000 (U.S.) is paid out at the industry standard 70% revenue share.  This applies to both paid and in-app purchases for the lifetime of the app.
• Developerscan set the price of their app starting at $1.49 (U.S.), using $.50 (U.S.) increments up to $5 (U.S.). Increments increase at higher prices.
• For more information, see here

Windows Store Terms and App Certification Requirements

• The Windows Store App Certification Requirements, The Windows Store Terms of Use and the App Developer Agreement have all now been made available here
• Developer will be free to use their own commerce and ad platforms in their apps. 
• Developers can test their apps today against technical requirements via the Application Certification Kit (ACK) immediately. 
• For details see “selling apps” on the Windows Dev Center.

Sign up to the Windows Store blog for regular updates: http://blogs.msdn.com/b/windowsstore

Additional resources:

• Preview of the Windows Store: http://channel9.msdn.com/posts/Previewing-The-Windows-Store
• Live blogging of the Preview at AllThingsDigital: http://allthingsd.com/20111206/microsoft-promises-windows-store-will-offer-a-bigger-bite-of-the-apple/