Hmmmn, that's a tough one.
On one hand I agree that it's good as far as pretty much guaranteeing no money would ever go missing if all the cash in your wallet was recorded and signed for. However in the same vein, I think it is a gross invasion of privacy and could lead to all sorts of problems. What happens if I start the day with $10 in my wallet then fish around in my bag for my lippy and low and behold find a fiver ... all of a sudden I am $5 up and should any money be missing - I'd be the one they'd blame. What about tips from passengers? I know my airline doesn't allow it and I'm always to embarrassed to accept tips anyway, but what about airlines that allow tips - how would that weigh in?
It's definitely a tough one. I just think it's a real shame that money goes missing in the first place. Fortunately it hasn't happened on any one of my flights *touch wood*, but it's happened to friends and they have been put through the wringer backwards in order to find the culprit! Turns out the money collected had actually been left on board in a cup in the galley cupboard. The next day a very lovely and honest cleaner bought it up to the Crewing Offices. No appology to the crew involved however ... hmmn.