Start up your 360 and your going to be prompted to do a system update to get the mew XBE dashboard. This is a mandatory install so you Arcade owners are going to need to get some kind of storage media to put this on.
I was expecting a long download, but it was probably about 20-30 seconds with a 90 second install. Very impressive! I usually have to update my PS3 overnight just for a patch let alone a completely new GUI.
I just built my first avatar and I'm ripping my first game to drive now and will tell you how it works later.