A couple of years ago I filled out an inflight survey, after I had a compaint about the lack of "new business" availability on a series of flights. (actually 4 longhauls in a row, on a route which had been advertised as being served by new business class).
About 4 weeks later I received a letter from CX HK with a letter and a stand-by oneway upgrade voucher enclosed. Nice gesture on behalf of CX and a great F flight for me from FRA-HKG !!