Back at digitalpoint, there was a thread with a question about getting penalized if you are using a shared ip address.

While google is forever silent about their algorithms, my personal experience do tell me that it has some value if you have your own ip address. I used to house some of my sites on a shared hosting account. There were a few hundred other sites housed on that server.

After about two years, I decided to buy myself a VPS to do some experiments and to support my increasing need for server resources. As I have my own IP address now, I was surprised how fast i was crawled by the search engines and how fast it was for me to be indexed in the search engines. All I can say is that , it was way faster than my experience with a shared hosting service.

So are these websites on a shared hosting doomed? Not at all. Remember, the search engine algorithms play around with a lot of variables. Even if one bad website is hosted in the same shared hosting as yours, you can always build up your site by having more excellent content, more backlinks, and better on-page seo.