There's no question, though, that the "Susan" of "Lazy Susan" derives from the common feminine name. The "Jew" of "Jew's harp", however, does not seem to derive from the term indicating a member of the particular ethnic/religious population in question. The capitalization of the 'j' is probably a relatively later confusion.

At least, that's what I gather from what I've read, which is all I know about the subject.