After reading the replies I am convinced that the proper course of action when writing code that might find its way to CPAN is to adhere to the lowest version of Perl that one is still likely to find in common use. At this point in time that is possibly 5.8.x but arguably 5.10.x might be a reasonable cutoff. (I am not aware of any major hosting provider that still has 5.8.x for a system perl at this time, but ...)

That being said, it should be obvious that when one is writing code that will be used in a private environment where there is full control over which perl is to be used then one should take full advantage of the features that allow for a better product. The question in my OP was aimed at those of us who on occasion (or regularly) contribute to CPAN in the hopes of making life a little bit easier for someone else as a way of saying "Thank you" to those who have gone before us.

Thank you all for your contributions to this discussion.