If you own many websites and those websites link to each other in an attempt to boost search engine rankings then being on a shared hosting server may actually benefit your cause.
If you have 3 domains on a dedicated server and they are linking to each other, they all have the same ip, and while this is not bad, it is also not good.
If you have 2 domains on a shared server and 1 on a dedicated server and they all link to each other then there is some benefit going on here.
A shared server with a few hundred or thousand websites could have many sites linking to each other, some of those may be owners linking to their own sites, and some of those may be others linking to other sites that just happen to be on the same ip address. So It is difficult for Google, or Yahoo, or Bing to penalize/link dampen those persons accurately. This assumes that you believe that search engines penalize sites for linking to their other sites. (i don’t think they do, at least anymore)
What is your thought on the subject?