I was deeply skeptical, too.

Wikipedia calls the "typewriter" unsubstantiated: http://en.wikipedia.org/wiki/QWERTY. It's repeated a lot, though! There's a link to a paper which discusses it in more detail: http://kanji.zinbun.kyoto-u.ac.jp/~yasuoka/publications/PreQ....

Anyway, Wikipedia spends some time discussing jams and so on, so perhaps that's legit.

The "prevent typebars from sticking" part is true -- though the myth claims that it tried to do so by slowing down the typist, which is BS. It tried to do so by making common key-pairs move to non competing typebars.