Upgrading CORE Perl Modules? Use UNINST=1!
This one is easy to miss if you only develop in Perl part-time. If you have to upgrade a CORE module (usually because another module needs that upgraded CORE module), then you need to add UNINST=1 to your make(1) invocation.
There are few things more aggravating than to "make install" several times with different tweaks only to always end up with the same, out-of-date module stubbornly still installed. All for the lack of an UNINST=1.