I know there have been other questions like that but (i.e. Can I use C++11 with Xcode?) but mostly related to older versions of Osx or xcode so they don\'t really seem to be
In Xcode 4.1 you can use the 'other' flags to get access to the compiler's C++0x support, such as it is (Actually I'm not sure what level it's at right now, and I can't check it right now). The latest version of clang have much better support than the version that was shipped with Xcode 4.1. Xcode 4.2 should have the updated compiler and added language and library selection options.
So, to get C++0x support in Xcode 4.1 add the flags -std=c++0x -stdlib=libc++ to the compiler and -stdlib=libc++ to the linker. You might also need -U__STRICT_ANSI__ on the compiler (apparently if __STRICT_ANSI__ is defined it triggers a bug in the system headers).