Awesome talk by Herb Sutter in "C++ and Beyond" "You don't know [blank] and [blank]": http://channel9.msdn.com/posts/C-and-Beyond-2012-Herb-Sutter...

As you can guess it is about const and mutable, and Herb speaks about this feature(or problem -- depending on how you see it).

C++98: const == logically const

C++11: const == thread-safe