Hum... some bad news now : there are still troubles (that make app crash), but once again, I can't get it to crash on my own computer. So... I'm going to look for someone that knows Cocoa, OpenGL, C++ and Obj-C and that is using an Intel Mac in order to find the mistake.
I can't drop code myself to find it because it never crashes. I dunno if someone here would be able to do this, anyway I'm also going to look for helpers on some other forums.