Changeset 62313 brings Boost.System into closer conformance with the C++0x working paper (and FCD) with regard to the system_category and generic_category interface. Because system_category and generic_category change from constants to functions returning references, this is a breaking change. The fix is to change uses of "system_category" to "system_category()", and "generic_category" to "generic_category()". See https://svn.boost.org/trac/boost/changeset/62313 AFAIK, the only Boost library this change breaks is filesystem. The changeset includes fixes for it. Asio also uses System, but in a way that does not break AFAICT. Before committing the change, I tested system, filesystem, and asio locally on Windows and Linux. But given the possibility of unintended consequences, I thought a heads up to the list might be useful. I'll try to keep a close eye on regression tests as they cycle, but if anyone has any problems, please let me know. Thanks, --Beman