Originally Posted by micker

Lets clarify here... Google _does not_ just throw around penalties for websites sharing IP addresses... Until IPv6 becomes standard, shared IP's are the norm for the great majority of websites, google understands that and does not penalize for that.

I think you most likely read an article about regarding backlink penalization from a small IP pool. This is something google will take into consideration, and can easily get you grey-barred or downlisted. If I have 300 backlinks and all of them are coming from multiple domains on the same IP, the algorithm _will_ assume you are spamming in an attempt to boost your PR. If make sure atleast 30% or more of your backlinks are coming from a variety of IP's and you should be safe. The more the merrier though.

Incidently, your list of SEO considerations failed to mention domain ownership length. Google's algorithm is currently giving quite a bit of weight to how long you have purchased your domain for. They are going on the assumption that a domain purchased for 1 year has a greater chance of being used solely for doorway/gateway/backlink spam, whereas a domain purchased for 5 years is most likely a legit website.