No, no, and no not for that reason.
It doesn’t matter if you put your content on the same servers, same IP, even the same domain. None of those are ranking factors. People that are doing illegal or black hat methods may need to hide their affiliation to prevent their entire network of malicious websites from getting de-indexed all at once. However, if you are following Google’s Webmaster guidelines then there is no need to be concerned about that.
If you do build a network of blogs, it might be advisable to spread them out over several hosts to avoid a single point of failure, but that’s got nothing to do with SEO, just a way to add robustness to your network.
I’m sure that there will be other opinions on this matter, but mine is time tested and true for me as well as many other webmasters. Many SEO novices are into Cargo Cult Science or what I like to call SEO mysticism. I prefer the tried and true scientific testing methods. So follow whichever advice you feel the most comfortable with, a little mysticism may not hurt your SEO, just your wallet.
