Microsoft has squeezed an extra 1GB onto new discs that developers can use. Avatar Kinect is said to be 'made ready' by this update too. Go grab it now.
You're prompted to download the new update once the console is powered on and connected to the Internet so there's no avoiding the future. Menu fonts are said to be a little smoother but most notably PayPal is expanding its presence.
The spring update reportedly takes a little while to download and apply.