Here's a great history of English mispronunciations that became the received pronunciations. The piece makes the important point that English has no canon, no unequivocal right way or wrong way of speaking -- a point that is often lost in Internet linguistic pedantry and literacy privilege.
I'm as guilty as anyone of thinking that my English is the best English, but the next time I wince at "nukular," I'll remind myself that "bird" started out as "brid" and "wasp" started out as "waps," but were mispronounced into common usage.
Adder, apron and umpire all used to start with an "n". Constructions like "A nadder" or "Mine napron" were so common the first letter was assumed to be part of the preceding word. Linguists call this kind of thing reanalysis or rebracketing.
Wasp used to be waps; bird used to be brid and horse used to be hros. Remember this when the next time you hear someone complaining about aks for ask or nucular for nuclear, or even perscription. It's called metathesis, and it's a very common, perfectly natural process.
8 pronunciation errors that made the English language what it is today [David Shariatmadari/Guardian]
(via Hacker News)
(Image: Double bitted felling axe, Wikimedia Commons/Luigizanasi CC-BY-SA)