That's an interesting and rather controversial question, and the answer involves a lot of nuances, including some guessing about how Google figures out whether two Web sites are related or not.

But let's start at the beginning. Just as every telephone on the planet has a unique numeric descriptor (its phone number), every computer hooked up to the Internet has its own unique numeric identifier too, the Internet Protocol (or IP) address.

You might have heard of TCP/IP? That's the "language" of the Internet itself, how information is sent from computer to computer in fractions of a second, making it remarkably simple to query a Web server in Romania from your house in Nederland and see the results seconds later, or to send email from Bogota while on holiday to your pal in Peking. The "TCP" part is the information encapsulation protocol, Transmission Control Protocol, and the IP is, as we've already mentioned, the Internet Protocol. Together they are the lifeblood of the Internet and the Web.

Just because each computer has a unique IP address, however, doesn't mean that each Web site or each domain name is assigned a unique IP address. In fact, Web site hosting companies will often have dozens, hundreds, or even thousands of different Web sites, each with a different domain name, all on a single server, and quite often, all with the same IP address.

Now let's get into your question!

If you are going to set up two Web sites for your company, with two different domains, should you configure things so that each has a different IP address?

This might seem odd to worry about, but many people believe that Google and other search engines are skeptical of links from one Web site to another if both exist on the same IP. Why? Because they believe it's a likely sign of people trying to game the search engine "page voting" algorithm to artificially boost the popularity of a particular site.

If each link to your page is a "vote", then you can see the draw of creating a few "extra" sites that just point back to your original content: more links = more votes = better results in the search engine, right? If so, then if you do have more than one site, having them on different IP addresses should help Google and related think that they aren't related.

The problem is that we don't really know exactly how Google works, so we don't have any way of ascertaining if the supposition of a shared IP being bad for SEO is true. I can say that anecdotally, all of my sites and domains share a single IP address on a server, and Google still seems to like my content.

I'm afraid that there really is no definitive answer to your question. I think that from the perspective of ease of management and simplicity of implementation that a server that shares IP addresses across multiple sites / domains is good. If you're paranoid, however, different servers at different hosting companies is an option I know that some people definitely use...

Either way, your best bet is to focus on producing great content and a compelling store with an obvious, overt value proposition, and you'll do much better in the long run than if you spend your effort tinkering under the hood to adjust for the latest SEO faddish theories.