I gave my steward $100 at the end of a 14 day cruise (for the 4 of us, 2 adults and 2 kids).
I thought he would have been delighted with that as I understood that people don't normally tip after paying the recommended amounts; or if they did, $50 seemed to be sum usually mentioned.
He seemed disappointed when i saw him later that day so I asked if he was happy with his tip. He was most reluctant to comment and said we should give him whatever pleases us. After some grilling on my part, he said that this was a bit on the low side and I gave him another 100 Euros (having run out of USD by then).
He mentioned that he services the cabins on his own while other cabins are allocated 2 stewards. So when new passengers come onboard, he has to pay another crew member to help him get the rooms ready in good time.