Google does use whois information - two years ago when buying DMOZ expireds was all the rage for backlinks they applied for and were recently approved as a Registrar. This gave them access to the whois with their bots, and so far all I can see that it has been used for has been for what some people call a sandbox - something I dont personally agree exists - but is an effect of a domain that someone uses being previously owned and a dampening effect for the new owner to prevent old links from counting.
(The "sandbox" appeared at the same time coincidently as the dampening effect for the prior registered domains so to me they have always just been the same thing)
As far as private registrations, I believe Matt Cutts mentioned that in his blog some time ago -
http://www.mattcutts.com/blog/false-whois-data/ and basically distinguished between fake info and private info for his suggestions for reporting domains.