type_traits uses integral_constant<bool,val> for true/false results which in turn inherits from mpl::bool_<val> so the two should be completely compatible with each other. Note that integral_constant is part of the TR1 and the next std, where as MPL is not, so type_traits won't be changing in this respect.
OK, so it's maybe me. I used a lot of type_traits and MPL meta-function as generator for static boolean that serves as templae overload selector like : template<class T, class EnableIf = is_integral<T>::type> struct foo; template<class T> struct foo<T,false_type> {}; and I found that having to manage both true_/false_ and true_type/false_type in various overload a bit hard, especially if a tempalte has two set of EnableIf,one using traits one using MPL. Is going with usign the ::value a better idea, (aka making EnableIf a bool parameter ?) Thanks anyway for your welcomed insight