Completely agree. By far the best way to reward crew for good service is with positive feedback, either via a feedback form on board, or by email to the airline afterwards. There is some statistic that people are far more likely to complain in writing than they are to give positive feedback. For this reason, positive reports are given alot more weight internally. This is especially true on ME airlines such as QR. I have done this on a few occassions on board towards the end of a flight and such gestures are very warmly received.

Also, much as I don't doubt the good natured sentiment behind gifting chocolates/pastries or whatever, this doesn't take into account any allergies the crew may have which could potentially cause an issue on board.