What Google has admitted to looking at is your linking profile. In many spammy situations we may be talking about two of one and a couple of another; but for most Webmasters the IP address profile of back links is not an issue. There is no way to know precisely when and how Google will look at your back link profile, but if you can judge at a glance that it covers almost as many domains as back links, you're probably okay without having to fuss over who is using which IP addresses. What do you think about this matter?