It's larger.
As a person who has switched from a 12" Dell XPS M1210 to a 13.3" MacBook back in 2007 to an iMac in 2008 plus a bunch of Hackintosh netbooks (Samsung NC10, MSI Wind U100, and Dell Inspiron Mini 9) to an iPad in April 2010 to the 11.6" MacBook Air just last month, I can tell you that the 11.6" screen size really is the sweet spot.
The 9" screens of the netbooks really felt cramped, from the screen to the keyboard, and the 13.3" notebooks I had was pushing it in terms of size and weight.
The iPad was a joy at 9.7" screen because it was held and used differently, but since I'm physically not as close to my Air, the 11.6" screen is perfect for its traditional notebook-style use and nearly kept that iPad form factor.
I really have to tell you, these guys at Apple really know their design, engineering, and practicality. It's really uncanny.