Template Metaprogramming - Difference Between Using Enum Hack and Static Const

I'm wondering what the difference is between using a static const and an enum hack when using template metaprogramming techniques.

EX: (Fibonacci via TMP)

template< int n > struct TMPFib {
  static const int val =
    TMPFib< n-1 >::val + TMPFib< n-2 >::val;
};

template<> struct TMPFib< 1 > {
  static const int val = 1;
};

template<> struct TMPFib< 0 > {
  static const int val = 0;
};

vs.

template< int n > struct TMPFib {
  enum {
    val = TMPFib< n-1 >::val + TMPFib< n-2 >::val
  };
};

template<> struct TMPFib< 1 > {
  enum { val = 1 };
};

template<> struct TMPFib< 0 > {
  enum { val = 0 };
};

Why use one over the other? I've read that the enum hack was used before static const was supported inside classes, but why use it now?