The Asus UX31 ultrabook is the 13-inch big brother to the UX21. It has the same thickness as the UX21 -- 0.67 inches -- and weighs in at 2.9 pounds. The all-aluminum wedge form factor is as fetching here as on the MacBook Air it is clearly emulating, down to the ventilation in the hinge. That hinge is strong and overall build quality is solid; we detected no body flex whatsoever when we picked it up. The glass trackpad seemed quite responsive with a loud click. We also liked that the LED-backlit display can be ramped all the way up to 1600 x 900, a satisfyingly large resolution for this screen size. The one downer is the keyboard, which has a similarly shallow travel and mushy feel as its little brother.
As for other specs, the UX31 adds an SD card slot to the the same array of ports found on the UX21: Mini-HDMI, Mini-DisplayPort, and 2 USB ports. The model we looked at had a Core i7 processor (clocked at 1.8GHz) as well as a 256GB SSD and 4GB of RAM. Those specs added up to a snappy experience, though we obviously weren't pushing it especially hard here. Both the UX21 and UX31 should be available later this month.
Hands-on pictures are after the break, including some shots comparing the UX31 to the UX21.