We'll just block on bugs that need solving before we're completely gcc4-happy.
sys-devel/gcc-4.1.1-r3, sys-kernel/linux-headers-2.6.19.2-r2, sys-libs/glibc-2.5 are now sparc stable for the 2007.0 release. kgcc64-4.1.1 is pending investigation about some possible issues with atyfb on newer kernels. This is NOT intended for regular users, just 2007.0 or dev/gcc-4.1.1 profile (and those may change). If someone wants to upgrade it'll probably have to rebuild everything.
I think we're done as far as we know.