I guess you might be worried about custom modules... Just back up all directories in you @INC path (that the one that gets printed out when perl can't find a module). Then upgrade.

Depending on how zealous your package manager is about cleaning up, the modules may or may not be there after the upgrade.

There is no reason to keep old modules if they are still available on CPAN. Backing them up in case somebody made a booboo with the new version of the module may be a good idea, though.

If it were me, I'd just do the upgrade, then deal with the 'missing module' errors as they come. Since perl is very clear about which modules it needs, it should be an easy task to reinstall them. I never knew there was a log of installed modules, but that would be a good way to do it.

____________________
Jeremy
I didn't believe in evil until I dated it.