Statements are executable and can have breakpoints set on them. Everything else can't.* Really the non-executable stuff in a header is no different than the non-executable stuff in a source file.

Basically once you've put a using namespace std; in your header, and someone has included your header, there's no way to undo the using. This can reduce your options when a name conflict occurs.

C++11 became an international standard late last year, and the C++ compiler purveyors are now busy implementing it. Many features and the entire new standard library are already shipping.