Good meditation; I've been there.

As you have observed, some versions of CPAN.pm install config information to a CPAN::Config in everybody's @INC path, in such a way as to prevent non-root users from using CPAN.pm. When this happens, I have removed (or simply moved out of the way) Config.pm, and rerun the configuration dialogue as a non-root user.

As an aside, I have a standard technique for dealing with CPAN on Unix systems. The first stage might be to upgrade the perl if the version is older than I am comfortable with. Otherwise, in most instances, the version of CPAN.pm that the installed Perl ships with is a bit old.

I install curl, ncftp and lynx, as these are tools that CPAN.pm will be asking for. And I install and configure sudo of course if it's not there.

As root, I upgrade CPAN.pm to the latest, going through all the configuration questions installing CPAN and leaving the CPAN shell. Then, as my non-root user I run cpan and go through the questions again, except this time, there are more of them, including questions about make install and ./build install. To these questions I use the sudo form of the command. Once this dialogue is complete, I can install Bundle::CPAN and any other modules I want, painlessly.