As everyone knows by now Microsoft issues two updates per year to the Xbox Live dashboard in an effort to improve its functionality.
The next update is currently scheduled to hit the Xbox360 in November, probably around the time the Playstation 3 launches in the USA, although that is just speculation.
One of the changes that will be immediately noticeable is that the Xbox Live Arcade screen is getting a makeover. It will now show an Xbox Live Arcade image for its loading screen. The icons themselves will be wider and generally just look better.
Another feature is the games screen will have a "Launchpad" option where you can play demos as well as XNA games. However, to play the XNA games, you must be a registered XNA user.