Decay Rate of Learned Skills

http://www.seriousplayconference.com/blog/learning-decays/

This is an interesting piece of research that illustrates something I have always wondered about.  How long do skills last once I "learn" them? 

If this is a repeatable measure or even close ( as I suspect it is for most "normal" skills) then it suggests that its only material you have learned or practiced in the past month and a half that define what you are "good at".  All your other skills have decayed or are decaying to some level of uselessness.

So the question becomes, how many skills can you practice and "keep sharp" in a rolling six week period?  Is this period fixed for everyone? Fixed for an individual? Are there ways to "fit more in" so they can be practised more quickly? (Simulation and training packs for individuals?)

Keep in mind that the figure of six weeks includes decay time; after 8 weeks the benefit of the learning was completely gone.

Makes you wonder about the value of formal education.