so many dreams ...
It does make a person look at an 8bit, 20MHz ATMega328 (etc.) and scratch his head wondering why a 32bit chip running at 700MHz only costs 3x as much. It's not that boards like the Raspberry PI are so powerful, but rather that the Arduino chips are so comparatively weak.Don't get me wrong, I understand that there's a place in the world for chips like the ATTiny. I'm just saying that there's a huge gap that exists between microcontrollers and microprocessors like the ARM.
I think the obvious question to ask is: "has anyone implemented an Arduino-compatibility layer on the RasPi yet?"
Chalk and cheese. When I get my Pi it will be at the other end of the USB cable to my Arduino. They aren't comparable because the Arduino is a micro-controller and the Pi is a computer. Your phone may be a computer, but your central heating boiler isn't - but it probably has something very akin to an Atmel 328 inside it. If you want a computer you get a Pi, you want a micro-controller you get an Arduino, the price / performance doesn't enter into it. You want chalk you buy chalk, if you want cheese you buy cheese.
The R Pi would be useless for what I do with an Arduino which involves a degree of timing, the Arduino can happily time things to a single millisecond (a single microsecond if you push it) and it has degree of accuracy (even the Uno with a ceramic oscillator), the R Pi having a powerful multitasking operating system couldn't be depended on at all, if some other stuff it was doing (like system maintainance) was guzzling the clock cycles what you thought should happen in 10 milliseconds might take 10 seconds. The puny 8 bit processor in the arduino only does the task in hand and it doesn't have a system to maintain.