Windows 8 C# code sample that asks for a review of the app after 5 launches

example.cs

// --------------------------------------------------
// Ask for a review after 5 starts of the Application
// --------------------------------------------------

// Variable to hold the number of time the app started
int startedCount = 0;
// Check if the variable was stored in the Roaming Settings before
if (Windows.Storage.ApplicationData.Current.RoamingSettings.Values.ContainsKey("startedCount"))
{
    // If so, read it in the variable
    startedCount = (int)Windows.Storage.ApplicationData.Current.RoamingSettings.Values["startedCount"];
}

// Increment the count by 1
startedCount++;
// And then save it in the Roaming Settings. Note that if the value pair was not
// created before, the method will create it automatically
Windows.Storage.ApplicationData.Current.RoamingSettings.Values["startedCount"] = startedCount;

// If the app was started 5 times
if (startedCount == 5)
{
    // Create a MessageDialog requesting a review
    var md = new Windows.UI.Popups.MessageDialog(
        "Thank you for using [App Name] for a while now, would you like to review this app?",
        "Please review my app");
    // Build the 2 potential responses using the Commands collection
    bool? reviewresult = null;
    md.Commands.Add(new Windows.UI.Popups.UICommand(
        "Yes", 
        new Windows.UI.Popups.UICommandInvokedHandler((cmd) => reviewresult = true)));
    md.Commands.Add(new Windows.UI.Popups.UICommand(
        "No",
        new Windows.UI.Popups.UICommandInvokedHandler((cmd) => reviewresult = false)));
    // Display the MessageBox asyncronously. ** Note that you may have to add the async
    // keyword to the OnLaunched event definition above
    await md.ShowAsync();

    // If the user agrees
    if (reviewresult == true)
    {
        // Find the FamilyName of the app package
        string familyName = Package.Current.Id.FamilyName;
        // Navigate to the store Review Page for the Application
        await Windows.System.Launcher.LaunchUriAsync(new Uri(
           string.Format("ms-windows-store:REVIEW?PFN={0}",
           familyName)));
    }
}