Statistician / social scientist Andrew Gelman of Columbia University has this paper on survey methods for dealing with zombies.
This is very timely. Around here, I've successfully introduced the term "zombie panelist" to refer to longitudinal respondents who seem to have dropped out of sample, but later return.
This leads to sentences in reports like this one from September 2009: "The zombies are a de minimis nuisance in processing an annual sample by month since it's only the annual boundary we need to worry about; they are going to be more serious when we are doing weekly maintenance."
And this email from a statistician at another firm: "In January, 2008 36 zombie households were added."
Were it not for research niceties like "make sure your operational definitions are compatible" I could provide Gelman with several hundred zombies for study.