As you may know, Apple has remove the Ethernet port from its Macbook Air and Macbook Pro with Retina Display. Though you can add a USB Ethernet adapter, that will of course occupy one of the two ‘precious’ USB ports. Kanex’s DualRole may be the perfect solution you are looking for, that it will offer you a Gigabit Ethernet without taking away USB port, but instead adds two more ports.
The 2-in-1 DualRole, as its name suggest, performs two duties. It combines USB 3.0 hub with a USB Ethernet adapter. It turns one USB port of your Macbook Air/Macbook Pro Retina into three USB ports for connecting more peripherals, and a Gigabit Ethernet port for wired network connection. The USB 3.0 ports are backwards compatible with USB 2.0, while the Ethernet port supports Wake-on-LAN, twisted pair crossover detection and auto-correction as well as Full-duplex with flow control and Half-duplex with backpressure operation.
The Kanex DualRole is USB-powered, but users can plug in an optional power adapter to provide more power to the USB 3.0 ports. You can get one for $69.