It depends on whose money I'm spending. If it's mine, I put the extra tip as zero unless they do something really exceptional.

If it's my employer's money, well, I'm sure there's a reason that hospitality employees love business travellers!

As an aside, I just got back from New Zealand and they don't tip down there, and the service is wonderful. Of course, that might be because the people are just so friendly down there that it's incredible, but I still loved it.