Last year C++0x turned into C++11 and finally it's becoming a viable option for C++ programmers. At the same time, FreeBSD had been stuck with gcc 4.2.1 - the last version of gcc under the more permissive GPLv2 - for about half a decade, so the announcement that Clang will be in the base system was pretty amazing. Until recently the new libc++ (which replaces GNU libstdc++) was not part of the base system, so compiling C++11 code with Clang wasn't possible on a stable FreeBSD system. Finally 9.1 RC1 adds the bits necessary, so I decided to upgrade one of our 9.0 systems to 9.1 RC1 and build a Clang only system, using C++11 and Clangs libc++ to compile all C++ code in the required ports, so we'll end up with a complete C++11 tool chain and finally compile our own code base using Clang.
I already identified problematic ports, so this endeavor will definitely require some time, effort and patching. I'll keep posting about milestones and obstacles I encountered in the process.