I think you just broke my brain…
(So has somebody run Zed Shaw's Fibbonacci sequence code on it yet?)
Of course, the Arduino board isn't limited to the Arduino programming environment. Hackers tend more towards programming the AVR directly, providing greater performance and environments more familiar to them.
I really like how easy it is to hack prototypes together with Arduino. I recently moved my own prototypes from PIC24 to a Teensy++ (a tiny little Arduino compatible board) and its made life so easy! Its a lot of fun to play with and the wealth of libraries makes prototyping a breeze. Just today I was tinkering with ultrasonic sensors and with bluetooth modules.
For end products, I'd use C and LUFA for atmels rather than Arduino (or a PIC24 if I want 16bit or some of the other fancy PIC24 features, like 40MHz Fcy on PIC24H! since I have no experience with non-8bit Atmel micros)