Mike Flynn has a great takedown of some of the common myths concerning the so-called Dark Ages. I've known generally about the gross exaggerations the stem mostly from Enlightenment era Protestants, Deists, and skeptics—sort of like how most of the horrors of the Spanish Inquisition can only be found in the histories of the English from the Elizabethan era on.
It's an entertaining read, if you're a history buff, and even if you're not. If you want to have your mind blown sometime, go read the comments Flynn leaves at John Wright's blog. The intellectual power of the two of them together causes my head to implode.