Improvements to the Xbox Guide.
Option to retain your saved games when you delete a profile.
Increased accuracy of "last time played."
Network configuration improvements for Xbox LiveŽ members in the Netherlands.
More detailed messaging for unreadable disk or region errors.
Only the first of those really happens to affect gameplay all that much, though it's an interesting time we live in when a console, typically thought of as a pretty static, unchanging firmware-crafted device, is getting online updates. That does seem to be the trend future consoles are heading towards, and is likely to become even more prevelant.