Thank you, Gwendo, for posting a topic that makes us think about. Here are the provisional results of my search and thought.
LET ALONE = NOT TO MENTION.
"let alone" is normally an idiom operating as a preposition and meaning "to say nothing of";
I think the idiom introduces a step further in the thought.
Lacking the courage, let alone the skills, to be effecitve (Webster's)
He can't read, let alone write (Robert & Collins)
We have no room for another house guest, let alone an entire family. [c. 1800] (Answers.com)
I cannot speak, let alone make a speech.
I couldn't walk, let alone stand up.
Lacking for time, let alone for knowledge, I though try to bring a follow-up to Gwendo's question.
All sentences I can hear, read or imagine bring a negative sense (not necessary a grammatical negation), as if "let alone" should mean "even less" (adverb)
I wonder whether one could hear something going this way: "He was offered a reward, let alone a special prize."
Whereas "not to mention" for sure hasn't that particularity of a LESS. the idiom just mean "In addition to, besides what's already been said." (http://www.answers.com/topic/not-to-mention)
She is a good girl, not to mention she is clever.
It took a lot of time, not to mention the cost.
I for one would rather say "He was offered a reward, not to mention a special prize."
To my mind, most usually, the idiom NEVER MIND doesn't share any meaning with the latter ones.
It means "don't care about it; it doesn't matter, don't worry about it; it makes no odds; ..."
Howerever I find in the Robert & Collins that use you for sure were thinking about "He can't walk, never mind run."
Never mind what I said here above, Gwendo, you possibly know more about that locutions. Tell us, please.
And if there is anyone out there who has got better information, I'd be pleased to know it.
Posts: 588
23 Oct. 2008