<p>Has anyone ever seen the storage class <code>auto</code> explicitly used in C/C++? If so, in what situation?</p>

auto is never useful in current C/C++ because all variables are implicitly auto. It is useful in C++0x, where it can replace the type declaration entirely - if you have a variable with an initial assignment, 'auto' will just make it the type of that assignment value, as in the comments.