i was pretty excited for the OP
and in a way i can see what captain crunchy is saying too, we don't want to manipulate our kids but i'm not entirely convinced it applies to the OP.
i have said to my kids that "i am disappointed in your behaviour" and i'm not too sure what i think about it. one the one hand, owning my own feelings by using I statements is more a reflection of me, and less of them, and secondly, when my kids are doing things they have been repeatedly asked NOT to (for whatever reason, safety, we're in a hurry, it's hurting someone etc etc) - and we're talking 5 times in the last 5 minutes to stop - then yes, i feel disappointed that they aren't listening.
i think it's good to express our feelings in a constructive way, we need to teach our kids it's okay to have feelings that are not all positive and that we can share them in a way that doesn't have to 'hurt' another person, and kids do need to realize that their action does impact other people and sometimes, it does impact others in a negative manner.
and you know, we are all human, i know i don't live up to the ideals of GD by any means even though i do my best. it was a lot easier when it was myself and my dd, now with 4 kids and a husband who works out of town 7 out of 12 days (which means an exhausted mama), you gotta celebrate the small successes because they are important and they inspire you to keep trying and have hope.