One on the nice feature coming with WP7's mango is "live tiles". You can create tiles directly from your application and update them from a background agent.

Here is the sample which creates a "secondary tile" for your application: 

//This is a .Net class named StandardTileData
var theTile= new StandardTileData
{
Title = "Secondary Tile", //The title
BackgroundImage = new Uri("FrontImage.jpg", UriKind.Relative),
Count = 12, //Notification number
BackTitle = "Back's page title", //The title of the back page
BackContent = "A text is nice here",
BackBackgroundImage = new Uri("backImage.jpg", UriKind.Relative)
};
// Add the live tile to the Home screen (will exit the app)
ShellTile.Create(new Uri("/MainPage.xaml", UriKind.Relative), theTile);

Now, you may want to generate a screenshot of your application (using WriteableBitmap) and use it as the tile background. This is possible !

To do so, you have to store the picture in a folder named "Shared/ShellContent" otherwise you will have an NotSupportedException throwned.

The URI to use will then look like this one : "isostore:/Shared/ShellContent/background.png". You can read this MSDN page for more information.

It takes me some minutes and Wilfried to figure this out, I hope this will save you this time !