When running "emerge clean", old distfiles tarballs should be removed along with the old package. If you've upgraded a package, and are cleaning out the old one, there's no sense in keeping the older tarball. Keeping one tarball in distfiles makes sense to me, and it might as well be the latest version installed. I realize that sometimes packages are downgraded, but that's pretty rare, I'd think. Perhaps add a make.conf variable to keep track of how many versions back you'd like to keep in distfiles. I.e. a value of 3 would keep the 3 latest versions in distfiles. I just wanted to point out that it'd make sense to clean out old tarballs with old packages, even more so when you've got AUTOCLEAN="yes".
*** This bug has been marked as a duplicate of 2567 ***
