This is something that's just really all over the board. Some people like to tip (or claim to) a lot extra, some people will tip some extra, and some will be content with just the auto gratuities. (And then of course you get those that want those removed).
Personally, I think it's hard to guide anyone what they should tip. If you leave the auto gratuities on, you've met any real obligation that you have to the crew. Beyond that, it's an entirely personal decision.
Typically, on a 7 day cruise, *if* I tip extra, I tend to do about $20 for the steward, $20 for our mai