At E3 we had some spirited discussion about whether the 360 was really smaller than Xbox 1. I in particular contended that it's not hulking and black, and the curved lines make it look smaller than it actually is.
Gizmodo has pictures of their review (retail and debug) unit - including it right next to an Xbox. It's smaller, yes, but it's not 10% smaller. There's also a pic next to the Gamecube and slimline PS2 just to drive the point home. Sucker is still pretty damn big :-)