Jon Biggar wrote:

Is there any package in Boost (or upcoming in the Boost review queue) that would let me create an output stream that clones its output to one or more underlying output streams?

Jonathan Turkanis's Iostream library, which is currently under review and has been mostly positively received, seems to make it pretty trivial to write such a thing - see http://lists.boost.org/MailArchives/boost/msg69799.php and http://lists.boost.org/MailArchives/boost/msg69827.php.