I figure that on a ship I deserve EXCELLENT service. I almost always mark it that way on the comment card.
If the ship decides to set the standard for an auto tip, then I figure they have made the determination for me. For normal EXCELLENT service, that is what I leave. It is usually less than our total tips were back in the envelope days, but the cruise line sets it so the crew should be satisfied with it.
On very very rare occasions, I have handed an extra $5 or even $10 to some particular crew member, usually not because they went especially beyond EXCELLENT service physically, but because their smiling and helpful attitude was something special.
On one recent cruise, I was appalled that the CD mentioned, not once but several times in his disembarkation talk on the TV, that the auto tip was a "minimum" tip and if you got good service you should be sure to add to it. I thought this was incredibly out of line, and I blasted him on my comment card for it.
What I will do, however, is be sure to mention the name of those who gave extra service on the comment card. I have been told again and again by crew members how important this is to them and how much the senior staff are impressed by a mention on a comment card. In fact, once we had a particularly good dining room team, and I mentioned to the waiter I was going to put both their names on the comment card. The waiter actually said, "Just put the assistant waiter. She is up for promotion, and a mention on a comment card will really help her get it."
That's the way I see it. Now I am going to get my popcorn, sit back, and watch the show ... ;o)