I got so fed up with Processing opening Arduino code that I modified the file extension mapping in my OS to make Arduino the default application for PDE files.
A short story:
A couple of weeks ago I got an email from a fellow student who was not able to get any arduino code to work.
I sent him the blink.pde and when he compiled he got all sorts of error messages, I simply thought something had happened to his Arduino install, and so, he reinstalled the IDE.
After some five more mail I realized he had been using the Processing IDE (Because he had used it in school, and ofcource it was set as default for .pde).
When he opened the blink.pde in Arduino IDE, everything was fine.
After this incident I searched around the arduino.cc for some information about this, so I could reference it to the student in trouble. I did however, not find anything.
I really hope this will be fixed soon