The Fine WW podcast had a show a couple months ago with an audiologist and two folks from ISOtunes where they talked about hearing protection in the workshop, including the difference and pros and cons of active vs passive, how to interpret the various types of noise reduction ratings, and other related issues. One of the interesting points they made was that muffs with active noise reduction are required to be tested at the ratings lab with the active noise reduction turned off, because the assumption is the batteries will die and often won't be replaced right away, especially on a job site.
Another interesting point concerned muffs that allow you to listen to music (or whatever) and the importance of limiting the volume to 85 db because that's the generally accepted maximum safe threshold for long term safe exposure.
Anyway, worth a listen if you're shopping for new hearing protection.
--I had my patience tested. I'm negative--