In the case of Mac OS X 64-bit, the natural thing to revisit is whether to use libstdc++ or libc++. libstdc++ is the tried-and-tested GCC 4.2 thing that we've been using ever since, but it is a dead end (due to Apple not upgrading past GCC 4.2 for license reasons) that will likely block future progress of using C++11 in LO (and I'd not be surprised if Apple drops it from a future OS X version). On the other hand, libc++ is clearly the way ahead on OS X, but somewhat less well tested with LO for now (only some individual developer builds having been configured to use it in the past).
Now, the good news appears to be that "Libc++ is specifically designed so that you can use it in the same process as libstdc++." [<http://clang-developers.42468.n3.nabble.com/Adopting-libc-hitting-problems-on-Mac-OS-X-td4027011.html>] That means that it hopefully works to stick with libstdc++ for LO 4.2 (and avoid any trouble switching this late in the release schedule), switch to libc++ for LO 4.3 say, and expect any native extensions using either of the two libraries to work with both flavors of LO. (And, given the assumption that Apple will eventually discontinue the support of libstdc++, recommend that native extensions---which there are none yet for Mac OS X 64-bit---use libc++.)
Other thoughts? Stephan