What breaking changes are introduced in C++11?

Question

I know that at least one of the changes in C++11 that will cause some old code to stop compiling: the introduction of explicit operator bool() in the standard l

Answer 1

struct x {
   x(int) {}
};

void f(auto x = 3) { }

int main() {
   f();
}

C++03: valid.

C++0x: error: parameter declared 'auto'