That is an extremely uncharitable interpretation, which seems likely to be unfounded in most cases. Papers take time to write (my most recent substantial paper took more than four years to write), while the job market is on a set schedule. If it is time to apply for jobs, but the paper is not yet written, it is completely understandable why someone would describe a paper as in preparation; they are making the best of an unfortunate piece of timing. Whether this is particularly helpful in a job application is another matter (see the various comments above for different opinions on this), but I don't think there's any reason for believing that this kind of entry on a CV is typically insincere.

Yours sincerely,

Matthew

In the case of textbooks or treatises,real life keeps getting in the way of finishing it.

Simple.

Andrew L.

Since this thread is turning into a de facto advice thread regarding the original question, let me say that my view is somewhat different from Kevin's: I would take "in preparation'' to mean that there is an announcement, that perhaps talks have been given, but there is no preprint (otherwise the paper would be listed as a preprint). I take "preprint'' to mean that a preprint exists, and is available somewhere (on the person's web-page, or on the arxiv) --- if I couldn't find the preprint after some straightforward searching, I would regard the CV as misleading.

As far as evaluating a candidate goes, listing a paper on a topic as "in preparation'' gives a sense of what the person is currently working on, what their ambitions are (in terms of what kind of problems they are trying to solve), and so gives useful information. On the other hand, this information doesn't really help in evaluating the strength of a candidate (say when attempting to rank competing candidates), because it is too ephemeral.

On the other hand, a preprint is a more substantial thing. If the candidate is in my field, or a nearby one, I can look at the preprint myself and form my own judgement, regardless of whether it has appeared somewhere. Also, a preprint can be read by letter writers, who may well comment on it in their letters. In other words, a preprint is part of the written record, and can carry weight just like any other part; it is missing the imprimatur of a journal, but this is just one aspect of evaluating a piece of work (one's own evaluation, and the evaluation of letter writers, being two other important aspects).

(For a more senior candidate, the issue of preprints is less relevant, since presumably these are only a small fraction of their written work. But for junior candidates, given the time that it can take for a paper to go from preprint form to acceptance in a journal, I don't think that it makes sense to ignore preprints a priori; they form data points which it may well be possible to evaluate.)

Certainly you can assume that the amount of credit given to you by listing a paper as "in preparation" on your CV (and not saying anything else about it) is essentially infinitesimal. If you want people to count it somehow, you should do something like posting a draft version on your webpage or at least an abstract / summary of results you have proven and/or want to prove. If dealing with someone else who lists this on their CV -- if you care about it, ask for more information.