I've just added a test program to ticket #2839: it fails on vc9. The ticket, I think, explains the problem pretty well, but I would like an expert to look at the code. I believe that the program is ill-formed, and it only works on gcc because the BOOST_WORKAROUND disables the code in question. The issue is that variant/detail/move.hpp:114 introduces a templated swap() overload in the same scope it will be called from, to allow move emulation. But, if the variant bounds a type defined in std::, like std::vector, then std::swap is another templated swap() and will be found by ADL. This makes the call ambiguous. My recommendation is that the move-emulation code be removed -- or enable_if'd, if that's possible -- until the generalised Boost.Move implementation is ready to be adopted. If we believe the code as it stands is correct, then I think the test case should be added to trunk and release, and additional BOOST_WORKAROUNDs added for all the compilers where the test fails. -- “Papa Hegel he say that all we learn from history is that we learn noth- hing from history. I know people who can't even learn from what happened this morning. Hegel must have been taking the long view.” -- John Brunner, ‘Stand on Zanzibar’