There is a fascinating thread happening now at Webmaster World regarding the public versus private availability of Whois information and the impact on search engine rankings.
The original poster had forgotten to renew his private Whois information and argued that his rankings dropped as a result. While it is difficult to say in no uncertain terms that the change did result in lower rankings, it is most certainly curious that Google is an official ICANN accredited registrar (but does not actually register any domains) which gives them access to Whois information in real time.
The result (if you believe the domain owner) has been a general devaluing of the inbound links. Other forum participants are not so sure. One poster said, "I think this is speculation more than specifically being tested. Some people have reported drops, such as SEOPTI. However, it is difficult to measure those drops and whether other factors did not come into play in terms of that drop that coincided with the automatic change."
And this poster was not alone. "I've not seen any impact of changing WHOIS information, from an edit or even via the adding or removal of 'privacy protection' from a domain name. I don't think it's improbable that WHOIS is a factor, but IMO it must be a small one, or one that can only be sufficiently amplified by other, unrelated, factors."
In the end, I think it is conceivable that Google would look for change in registrar data, when it correlates to a drastic change on the website. Best practice in this instance might be that if you buy a site from someone, you should wait a while before changing the content drastically if you change the registrar data right away (as you should).