Raspberry Pi now on available for bulk order (opens in new tab)

From what I gather (from having used neither yet) but from my PoV: * The Pi is more capable out of the box but more expensive (than the basic Arduino models). They are both essentially computer-on-a-chip units congregating on the same point from two different places (at least in respect to where you could use either for the job): The Arduinos are trying to be advanced microcontroller boards that are relatively easy to develop for, and the Pi is trying to be a full PC-on-a-board that runs a stock OS (potentially lowering the programming learning curve considerably) that also has features meaning it can be used in many contexts there a microcontroller like an Arduino would be considered too.

* If you are working on something as a one-off the Pi is probably the better option as it is more flexible (if nothing else you've got a spare little PC to use when the project is done unless it becomes a permenant installation).

* For something you might make in bulk, an Arduino is probably more cost effective (though you need to account for the learning curve) and will consume less power (though if you are driving motors the power draw by the controller might not be your significant issue in that area). The price of the Arduino units has more room to drop either due to bulk purchasing or simply due to things getting cheaper over time, basically because the Pi contains more hardware.

* Of course the learning curve might be the point. You might learn more from playing with the Arduino.

* From the microcontroller PoV there is a lot of existing documentation and projects to crib from out there for the Arduino which do not exist for the Pi yet. From the full mini-PC PoV there are things the Arduino simply won't be able to do.