Two weeks ago I presented at DevConnections the talk "AMS10: Developing and Deploying for the Windows Web App Gallery", here are the slides.
Download the Web Application Gallery Talk slides here.
A few final links:
Microsoft Web Platform: http://www.microsoft.com/web/
Download Web PI: http://www.microsoft.com/web/downloads/platform.aspx
Submit your Applications at: http://www.microsoft.com/web/gallery/developer.aspx