To me, CPAN Pollution is when people upload their module without sufficient thought put into its distribution. Lacks documentation, little or no test scripts, poorly-defined dependecies, or (as you mentioned) replicates functionality that has already been done. At times, this overlapping functionality is fine, since the authors may not approach the problem in exactly the same way, thus making one better than the other in certain situations. Other times, the two are nearly identical, which is just annoying (how many tied hashes implementing locked keys do we really need?)