My loyal reader Jez asks a very interesting question. I am sure the same question is on the minds of others in the same situation.
Finally, I am in the process of creating multiple sites around a similar theme. I have unique content for all sites, and will host on different servers in Europe and the US, however the whois for each domain will show my name (The company I used does not allow me to hide this info). Is the common whois likely to make much difference when I begin cross linking the sites?
Cross linking (or reciprocal linking) in a small scale (maybe 10 to 15 sites maximum) should not be a major concern. I've seen many sites do it and they are ranking in highly competitive phrases. Most of their link juice comes from non-cross-linked sites though.
When you try to do this on a massive scale, things start to get interesting. I know this from experience.
Back in 2003 and 2004, I managed to get a couple of my sites ranking on Google for "Viagra" and most variations. That is one of the most competitive industries, because you make really good money as an affiliate. I got those rankings through link exchanges exclusively. Being a developer, I created scripts to 'borrow' links from my competitors link directories and later traded links with my sites. When I hit the 5,000 links mark, my sites got banned and I dropped in all my rankings. Back then, Google was not as sophisticated as it is now.
Later, I carefully studied competitors that were doing a more advanced type of cross linking. They created large networks of sites that they owned, and they created complex inter linking structures to boost the rank of a few of their sites for highly competitive terms. Pair.com was a common web host as they provided IP address in different class C blocks.
That worked well for a while–until Google became a registrar. It is illegal to use fake domain registration information, and by having access to the domain ownership information Google could more easily identify complex cross linking. I think they became a registrar with that sole purpose. I don't see them selling domains in the future. They haven't yet. Have they?
Making your cross linked domains' registration private won't help much either. I think registrars have access to the real information anyways, but even if I am wrong, it would be suspicious for your site to have all inbound links coming from private registrations.
There are far more complex cross linking schemes where there are a few owners cooperating in the creation of massive collection of websites with well planned link boosting structures. The funny thing is that search engine researchers have already identified most of them. Check the paper "Link Spam Alliances", it is a very interesting read. So, If you want to cross link on a massive scale, you better have a very intricate and complex linking plan to avoid detection.