louieramos - 1:35 am on Sep 7, 2011 (gmt 0)
Based on experience with my current client, he's got a new .eu site hosted in the US and we are optimising his website on google uk. After a couple of months I was able to get him on Page 3 for his money keyword and remained there for a while. I got him to change host from US to UK and get a dedicated IP for his website, which he did.
2-3 weeks later his ranking climbed from 30 to 11 for his money keyword, and now 4 weeks later he is in the Top 10. I can't say 100% that IP affects rankings, but based on my experience it did.