search engines and pop-ups

We have a one-time (cookie-controlled) pop-up survey on our web site.
That is, when a user requests any page of the site, if s/he does not
have the survey cookie, the survey pops up. The survey cookie gets
written whether or not the user actually submits the survey, so under
normal circumstances (i.e., cookies turned on), the user only sees the
survey once.

Let's not get into a discussion of whether or not this is a good idea
from a usability standpoint, please... ;-)

The question at hand is: does anyone know whether having this kind of
pop-up survey will interfere with/confuse search engine spiders? We've
been working with some SE rankings consultants, and they've said it
*might* cause problems, but they don't know for sure.

Anyone have any hard data? Personal experience? Hearsay from your
neighbor's niece's best friend's milkman?

Thanks.

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