I am always banging on about ending well. For example I have recently been working for my old agency on a freelance basis. And although this has been a bit weird at times, it has generally been good fun.
I consciously tried to end as well as I could when I left a few months ago, and this has already paid off with a nice bit of freelance work from them lately. It really is a no-brainer as far as I’m concerned. I can’t understand people who don’t peform once they have handed their notice in. Just makes no sense any way you look at it – from your own pride in your abilities, or from the perspective of the contacts you may rely on in future.