The question about IP address and SEO is revisited time and time again. How beneficial is having a shared IP versus a dedicated IP? A Search Engine Watch Forums thread tackles this question.
1. What happens when one web site gets banned and in doing so penalizing the IP?
2. Is it fair that a web site using ethical SEO techniques is affected because it is being hosted in a "bad" neighborhood?
3. Does interlinking websites on the the same shared IP cause search engines to view them as a cluster and consequently loose link weight? i.e. links originating from a single C Block.
A few observations have been thrown out. A number of comments have been mentioned to reflect that Google is not as concerned about the IP address and focuses more on the domain name. However, it is observed that Google would rather you not link to the same sites if they reside on the same C-class.
Another person quotes Google:
"Actually, Google handles virtually hosted domains and their links just the same as domains on unique IP addresses. If your ISP does virtual hosting correctly, you'll never see a difference between the two cases. We do see a small percentage of ISPs every month that misconfigure their virtual hosting, which might account for this persistent misperception--thanks for giving me the chance to dispel a myth!"
-Google Director of Technology Craig Silverstein Slashdot interview
Ian McAnerin, moderator, adds that a shared IP is fine if you do not do anything shady:
For the average site, my experience is that it really doesn't matter if it's shared or not. It only becomes an issue if you begin to push the spam envelope, at which point I would suggest you have other problems other than your IP...
I invite you to read a blog post from my BFF Lisa that was written two months ago that also addresses this question. In the post, Lisa says that it's best to be on a dedicated IP.
Forum discussion at Search Engine Watch Forums.