Kymboed, a clone is an exact copy of the plant it was taken from. Nothing is lost in the cloning process. The only bit of truth to what GreenLeaf420 is saying is that over the course of hundreds of clone generations some genetic degradation can occur. But it's hard to imagine an amateur grower encountering that problem.

There are other factors that can attribute to clones losing their vigor, but if the plants are healthy then something else is contributing to the perceived lack of potency.