A common SEO related discussion topic is about whether using shared IP addresses negatively influence search rankings.

It seems that SEO's go round and round about the issue, so I decided to take a look at some real-life rankings to see if there is factual evidence that using a shared IP will actually harm your rankings. While I only looked at two search phrases ("valentines day" and "free valentines day ecard") on four search engines (Google, Yahoo!, Live.com, and Ask), it's enough evidence for me to conclude that there is no SEO-related reason to not use shared hosting.

A little background might be helpful. Shared IP's (often called virtual IP's) are those that host multiple sites while dedicated IP's (often called static IP's) feature one website exclusively. 

Using domaintools.com's reverse IP lookup I was able to determine the number of sites that were listed on each IP (reverse IP is an easy way to find all the domains hosted on a given IP address). While by pure definition if you have more than one website on an IP address, you could be considered to be on a shared IP, I noticed that some websites designated as having more than one website on an IP were actually all owned by one company (e.g. wilstar.com, proflowers.com). While still sharing an IP, no third parties are hosted on their IP in question but for our purposes here are still designated as being "shared". Another interesting phenomenon was that while double checking which domains were on a shared IP with MyIPneighbors.com, sub-domains were counted separately.

Just a side note - to avoid creating too long a list of sites, I have removed many of the duplicates found on each of the four search engines queried.