I'm totally in love with this compiler. It's so great. C++ code compiles quite a bit faster than it did in gcc 3.3.3, and the runtime speeds are amazingly faster.
I know the runtime speeds are faster on x86, but I'm not sure by how much. But on AMD64 platform the runtime speeds are an incredible increase in speed over what they were in the last compiler. They added -march=k8 to 3.4, and apparently that improves a lot of stuff.