An old marketing technique for dominating shelf-space in a store is to come out with more brands and products. Perhaps the same applies to websites. If you want to rank well and dominate a category to reinforce and hedge against a competitor creeping in down the road, perhaps it's wise to make multiple websites. However, does anyone know if Google analyzes whois data OR Google Analytics data OR Google webmaster data to identify the owner? Perhaps would Google penalize these sites if they know the multiple websites have the same owner in the same category? Thoughts?
Not sure but I think it is best to keep anything that you think could harm you away from Google. Its a good idea to have a few sites if in a profitable niche to dominate the top but best to protect yourself as if you do get penalised both sites may go!!! So, privacy whois, seperate IP's different content, different site structure/theme etc.
I believe Google does review whois data to try and find connections between websites, but just because a single person owns similar websites it does not mean they will be penalized. If both sites have unique quality content and are useful to users there is no reason that they both cannot rank well. Issues can arise if similar sites do not have unique content or are used only for inter linking purposes.
I wouldn't recommend this, if there's any amount of cross linking or links pointing to the same URLs, duplicate content or similar site structures, you may get flagged by Google. I've even heard Google having problems sometimes with different domain extensions of the same company, because of the similarity in site content and structure.