Mark Arteaga

If you are developing applications for Windows Phone 7 you might want to check out the Windows Phone 7 Application Certification Requirements document that is available and read through it. 

Here are a few items that I think may be potential gotchas when getting your app certified for Marketplace

• 4.1.1 List of Package Requirements
  The maximum size of the XAP package file is 500 MB.
  
• 5.1.1 Multiple Devices Support
  The application must run on any Windows Phone 7 device, regardless of model, screen size, keyboard hardware, and manufacturer.
  
• 5.1.2 Application Termination
  The application must handle exceptions raised by the .NET Framework and not terminate unexpectedly. During the certification process, the application is monitored for unexpected termination. An application that terminates unexpectedly fails certification.
  
  When handling exceptions, an application must provide a user-friendly error message. You may present a message that is relevant to the context of the application or use a Microsoft provided error message. The application must continue to run and remain responsive to user input after the exception is handled.
  
  An application that displays generic or unhelpful error messages will fail certification.
  
• 5.1.3 Application Does not Hang
  The application must not become unresponsive to user input because of an operation within the application. For time consuming activities such as downloading data over network connections, the application must display a visual progress indicator. When there is a visual progress indicator, you must implement a UI element that provides the user with an option to cancel the time consuming activity.
  
• 5.2.1 Launch Time
• The application must render the first screen within 5 seconds after launch.To meet this requirement, Microsoft recommends that the application provides a splash screen image in a file called SplashScreenImage.jpg in the root of the XAP package.
• Within 20 seconds after launch, the application must be responsive to user input.
  
• 5.2.3 Use of Back Button
• Pressing the Back button from the first screen of an application must exit the application.
• Pressing the Back button must return the application to the previous page. If the current page displays a context menu or a dialog, the pressing of the Back button must close the menu or dialog and cancel the backward navigation to the previous page.
  
• 6.2 Push Notifications Application
• 6.2.1 Configurable Functionality
  In the UI or settings menu, the application must provide the user with the ability to independently disable toast or tile notifications.
• 6.2.2 Initial Push Notifications Functionality
  On first use of HttpNotificationChannel.BindtoShellToast or HttpNotificationChannel.BindToShellTile methods, the application must ask the user for explicit permission to receive Push Notification Service.
  
• 6.3 Applications Running under a Locked Screen
• 6.3.1 Configurable Functionality
  In the UI or settings menu, an application must provide the user with the ability to prevent the application from running under a locked screen.
• 6.3.2 Launch Configuration of Running under a Locked Screen
  On first use of ApplicationIdleDetectionMode, an application must ask the user for explicit permission to run under a locked screen.

These are the things that jump out at me that could potentially have your application fail certification.  Have you started preparing for certification?  Anything else jump out?  Comment below or ping me via twitter.com/MarkArteaga.