My Garner's Usage Tip of the Day brought this interesting entry:
joust. The traditional view is that this word should be pronounced either /juhst/ or /joost/. See NBC Handbook of Pronunciation 264 (4th ed. 1984) (listing only /juhst/); William H.P. Phyfe, 20,000 Words Often Mispronounced 421 (1937) (listing only /juhst/ and /joost/). But almost all Americans say /jowst/; this pronunciation must be considered not just acceptable, but -- because of its overwhelming prevalence, coupled with no good reason for opposing it -- preferable. Let the orthoepic jousting cease.
I had no idea that joust was once pronounced any other way. The OED lists jowst as the current pronunciation.
And if you are wondering, orthoepic means "of or relating to orthoepy," which is "That branch of linguistics which deals with pronunciation," according to the OED.