run `zcat /proc/config.gz > ~/kernelconfig` (i believe that's the right filename for the average Gentoo kernel; haven't booted Gentoo in a long time) and you'll end up with a full list of all the options you chose for your currently running kernel.
This shows all the config options. Options change from kernel to kernel so doing a simple diff does not always reveal the user's intentional config changes. Otherwise gentoo is painless.. in the long term.
