The Arduino and Raspberry Pi are 2 very different things, but are both common among hackers and makers. The Raspberry Pi does have GPIO pins for controlling and reading the physical world, however the Arduino is the board more suited for that job.
The Arduberry works straight away with an existing Pi, but a customized version of the Raspbian distro will be available with the Arduino software bundled in. As it is a shield for the Pi, you can just slip the Arduberry onto your Pi, and upload code directly from the Pi. Most code will work out-of-the-box, but at most, a slight modification will be needed for things like using Analog pins.
Power comes from the Raspberry Pi, but for more power hungry projects, a 5V power supply can be connected via either the power connector or the micro USB slot.
Arduberry is a pretty interesting concept; it allows you to leverage the best of both worlds, and create some powerful, standalone projects. If you have an Arduino project, controlled by a shield, and you want the power of a Pi for number crunching, networking, or other tasks the Arduino can’t handle, the Arduberry could well solve your problem.
The end result is similar to the UDOO, and other Arduino/Pi hybrids, but easily comes apart if you need it to.
Dexter Industries is looking for funding for the Arduberry via its Kickstarter campaign. For $23 you can get your very own Arduberry, assembled and delivered. For $84 you get the Arduberry, a Raspberry Pi, the custom OS and a power supply: you can’t go wrong for your first foray into Pi/Linux from Arduino-ing.