Do private domains hurt your ability to rank in search engines? This is a question that I have not seen asked, but I think it deserves consideration. Search engines use many factors to determine whether to trust a website and the links to a website, and I believe whether or not a domain is registered privately contributes to these factors.
1and1 the popular web host and domain registrar has been offering private registrations with their $5.99 domains for quite a while and I have been taking them up on the offer with a few of my domains. In reality domain names are not very private, but the registrations force someone need to a reason to discover the domain owner. Spammers of every fashion have an obvious reason to use private domain registrations.
Because of the number of domains registered with the same data and the percentage of domains that are spam with that registration data, could all private domains be taking a hit in the rankings?
We know that Google has started using a number of domain factors including the length of domain registration, nameserver, and whois data as factors in their algorithm.
Search engines use heuristic pre-processing of links to adjust the recommendation values for each link. This reduces the weight of internal links, reciprocal links, site wide links, and links which are likely to be advertisements or otherwise nepotistic.
At this point the search engine compares the domain name, IP address, dns server and other whois data of the pages linking and being linked, which helps determine if they have a relationship. While thousands of unrelated websites are often hosted on the same machine or use the same nameservers, whois data is particularly indicative of a relationship because of the uniqueness of legitimate mailing addresses.
Two unrelated pages on websites of private domains could end up with very similar whois data and the same registrant mailing address.