USA, if there is enough detail in the letter, and the manager receiving it feels so inclined, they can always nominate the crew member for an award under the QF employee program (Excel).
So if a crew member has done something specific that you think is worth a mention, include it in your letter. (E.g. crew member provide x assistance during a delay). Then the manager can use that letter as a nomination on your behalf. It has to be specific though, it can't just be 'I have had so-and-so on three of my flights and they have been lovely' kind of thing...
Not sure if it happens often that managers bother but I do know it has happened once or twice!
Hope this helps!
(I agree this thread is getting confusing!)