I've recently upgraded to a Mac with 64bit firmware and Snow Leopard. I've noticed all applications compiled with g++ now default to 64 bit libs (x86_64), including boost. Thanks by the way for the fixes to boost 1.41 that allow successful 3- way arch compilation on osx again! Now I'm trying to just build two- way arches. I'm now trying to compile boost (I happen to be using trunk), and am noticing that passing 'address-model-32_64' does not seem to have the effect I'd expect. If the flag is passed the only affect I notice is that the build directories include it 'address-model-32_64' in the path, but notably the '-arch -i386 -arch x86_64' flags are not properly added to the CXXFLAGS and LINKFLAGS. Therefore the compiled dynamic libraries are still single architecture, x86_64. Passing 'architecture=combined' does prompt these flags, but includes the 'arch ppc' flag as well which I don't want. So, is it a bug that using address-model alone does not work or am I am misunderstanding something? Thanks for any clarification. Cheers, Dane