What's the reason for ditching them? You don't think they will ever buy? You have other clients? You did a cost analysis and the payoff if they buy a house does not justify the work?
What did they say when you asked them why they hadn't made an offer?
You forgot to include pocahontas in your list:
http://failblog.org/2010/01/10/avatar-plot-fail/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+failblog+%28The+FAIL+Blog+-+Fail+Pictures+%26+Videos+at+Failblog.ORG%29