Last Friday's Garner's Usage Tip of the Day was pretty interesting:
derring-do. "Derring-do" (= daring action) derives, according to the Oxford English Dictionary, from a "chain of misunderstandings and errors." Originally, the term was "dorryng do," a verb phrase meaning "daring to do." A 16th-century misprint in the poetry of John Lydgate (ca. 1370-1450) made it "derrynge do," which Spenser (1579) misunderstood and used as a noun phrase meaning "manhood, chivalry." Then Sir Walter Scott popularized the phrase in Ivanhoe (1820) with the spelling "derring-do," and this has been the settled spelling ever since. But because of its historical and modern associations with "daring," writers often use the erroneous spelling "daring-do."