What are these numbers on the right side of my Windows Phone Silverlight app?

That’s the frame rate counter for the emulator / phone that is on by default whenever you debug. To turn it off, go to App.xaml.cs and comment this line out:

Application.Current.Host.Settings.EnableFrameRateCounter = true;

For more information on what the numbers mean (they can be pretty helpful for tracking app performance), see Jeff Wilcox’s post on this.