The script writes the initrd to /usr/share/genkernel/pkg/x86/cpio. Please put the output in the kernel source dir or /usr/src etc.
Actually, the initramfs and all the intermediate cache files should probably be written to /var/cache/genkernel (or some subfolder, like /var/cache/genkerne/<arch> for LFS complicance, plus it makes it much easier to clear the cache when genkernel is updated (as there is no switch to purge the cache)
There's no need to CC people that are maintainers and on the alias. Anyway, patches are welcome. It cannot be made to write to the kernel directory, though, unless it also completely utilizes KBUILD_OUTPUT. It would probably be preferable to stick it somewhere else under /var/tmp or /var/cache, as Salah pointed out. Since this isn't a bug, per se, I'm changing to enhancement.
Well, this has actually been configurable (CACHE_DIR) in genkernel for a *very* long time now. That being said, I've changed the default in SVN to point to /var/cache/genkernel/%%ARCH%% instead of /usr/share/genkernel/pkg/%%ARCH%% where it used to be set.
This is fixed in genkernel 3.4.7 which is now in the tree.